A comprehensive review of prioritised interventions to improve the health and wellbeing of persons with lived experience of homelessness

Abstract

Background

Homelessness has emerged as a public health priority, with growing numbers of vulnerable populations despite advances in social welfare. In February 2020, the United Nations passed a historic resolution, identifying the need to adopt social‐protection systems and ensure access to safe and affordable housing for all. The establishment of housing stability is a critical outcome that intersects with other social inequities. Prior research has shown that in comparison to the general population, people experiencing homelessness have higher rates of infectious diseases, chronic illnesses, and mental‐health disorders, along with disproportionately poorer outcomes. Hence, there is an urgent need to identify effective interventions to improve the lives of people living with homelessness.

Objectives

The objective of this systematic review is to identify, appraise, and synthesise the best available evidence on the benefits and cost‐effectiveness of interventions to improve the health and social outcomes of people experiencing homelessness.

Search Methods

In consultation with an information scientist, we searched nine bibliographic databases, including Medline, EMBASE, and Cochrane CENTRAL, from database inception to February 10, 2020 using keywords and MeSH terms. We conducted a focused grey literature search and consulted experts for additional studies.

Selection Criteria

Teams of two reviewers independently screened studies against our inclusion criteria. We included randomised control trials (RCTs) and quasi‐experimental studies conducted among populations experiencing homelessness in high‐income countries. Eligible interventions included permanent supportive housing (PSH), income assistance, standard case management (SCM), peer support, mental health interventions such as assertive community treatment (ACT), intensive case management (ICM), critical time intervention (CTI) and injectable antipsychotics, and substance‐use interventions, including supervised consumption facilities (SCFs), managed alcohol programmes and opioid agonist therapy. Outcomes of interest were housing stability, mental health, quality of life, substance use, hospitalisations, employment and income.

Data Collection and Analysis

Teams of two reviewers extracted data in duplicate and independently. We assessed risk of bias using the Cochrane Risk of Bias tool. We performed our statistical analyses using RevMan 5.3. For dichotomous data, we used odds ratios and risk ratios with 95% confidence intervals. For continuous data, we used the mean difference (MD) with a 95% CI if the outcomes were measured in the same way between trials. We used the standardised mean difference with a 95% CI to combine trials that measured the same outcome but used different methods of measurement. Whenever possible, we pooled effect estimates using a random‐effects model.

Main Results

The search resulted in 15,889 citations. We included 86 studies (128 citations) that examined the effectiveness and/or cost‐effectiveness of interventions for people with lived experience of homelessness. Studies were conducted in the United States (73), Canada (8), United Kingdom (2), the Netherlands (2) and Australia (1). The studies were of low to moderate certainty, with several concerns regarding the risk of bias. PSH was found to have significant benefits on housing stability as compared to usual care. These benefits impacted both high‐ and moderate‐needs populations with significant cimorbid mental illness and substance‐use disorders. PSH may also reduce emergency department visits and days spent hospitalised. Most studies found no significant benefit of PSH on mental‐health or substance‐use outcomes. The effect on quality of life was also mixed and unclear. In one study, PSH resulted in lower odds of obtaining employment. The effect on income showed no significant differences. Income assistance appeared to have some benefits in improving housing stability, particularly in the form of rental subsidies. Although short‐term improvement in depression and perceived stress levels were reported, no evidence of the long‐term effect on mental health measures was found. No consistent impact on the outcomes of quality of life, substance use, hospitalisations, employment status, or earned income could be detected when compared with usual services. SCM interventions may have a small beneficial effect on housing stability, though results were mixed. Results for peer support interventions were also mixed, though no benefit was noted in housing stability specifically. Mental health interventions (ICM, ACT, CTI) appeared to reduce the number of days homeless and had varied effects on psychiatric symptoms, quality of life, and substance use over time. Cost analyses of PSH interventions reported mixed results. Seven studies showed that PSH interventions were associated with increased cost to payers and that the cost of the interventions were only partially offset by savings in medical‐ and social‐services costs. Six studies revealed that PSH interventions saved the payers money. Two studies focused on the cost‐effectiveness of income‐assistance interventions. For each additional day housed, clients who received income assistance incurred additional costs of US$45 (95% CI, −$19, −$108) from the societal perspective. In addition, the benefits gained from temporary financial assistance were found to outweigh the costs, with a net savings of US$20,548. The economic implications of case management interventions (SCM, ICM, ACT, CTI) was highly uncertain. SCM clients were found to incur higher costs than those receiving the usual care. For ICM, all included studies suggested that the intervention may be cost‐offset or cost‐effective. Regarding ACT, included studies consistently revealed that ACT saved payers money and improved health outcomes than usual care. Despite having comparable costs (US$52,574 vs. US$51,749), CTI led to greater nonhomeless nights (508 vs. 450 nights) compared to usual services.

Authors' Conclusions

PSH interventions improved housing stability for people living with homelessness. High‐intensity case management and income‐assistance interventions may also benefit housing stability. The majority of included interventions inconsistently detected benefits for mental health, quality of life, substance use, employment and income. These results have important implications for public health, social policy, and community programme implementation. The COVID‐19 pandemic has highlighted the urgent need to tackle systemic inequality and address social determinants of health. Our review provides timely evidence on PSH, income assistance, and mental health interventions as a means of improving housing stability. PSH has major cost and policy implications and this approach could play a key role in ending homelessness. Evidence‐based reviews like this one can guide practice and outcome research and contribute to advancing international networks committed to solving homelessness.

PLAIN LANGUAGE SUMMARY

Housing, income assistance, and case management improve housing outcomes for persons with lived experience of homelessness

Permanent supportive housing (PSH) interventions appear to improve short‐ and long‐term housing stability for persons with lived experience of homelessness. Income assistance and intensive mental health interventions show moderate benefits in housing outcomes, and evidence on standardised case management suggests potential to improve housing stability. Peer support alone does not impact housing stability. Inconsistent results on mental health, substance use and other social outcomes require additional research.

What is this review about?

Homelessness greatly magnifies morbidity and mortality and worsens preventable health and social inequities. We present evidence on a wide range of interventions targeting homelessness: PSH; income assistance; standard case management (SCM) and peer support; mental health interventions such as assertive community treatment (ACT), intensive case management (ICM), critical time intervention (CTI), and injectable antipsychotics; and substance use interventions such as SCFs, managed alcohol programmes (MAPs) and pharmacological interventions for opioid use disorders. What is the aim of this review? This systematic review and meta‐analysis examines the effects of a broad range of interventions on housing stability, mental health, quality of life, substance use, hospitalisations and health service utilisation, as well as employment and income among individuals with lived experience of homelessness.

What studies are included?

We included 86 studies across 128 publications among individuals with lived experience of homelessness. The vast majority of studies followed a randomised controlled design. Most took place in the United States (73). The rest were undertaken in Canada (8), the UK (2), the Netherlands (2) and Australia (1).

What are the main findings of this review?

Studies on housing interventions showed significant improvements in housing stability, with potential sustained benefit for up to 5.4 years. Income assistance interventions also appeared to be effective in improving housing outcomes. SCM carried the potential to improve housing, with mixed evidence suggesting its added benefit, whereas peer support programmes demonstrated no impact on housing relative to usual care.

Intensive mental health interventions demonstrated moderate improvements in housing stability and often worked in synergy with permanent housing.

Cost‐analysis studies of housing interventions reported mixed economic results. Income assistance was associated with increased costs that were offset by its added benefits. Intensive mental health interventions, such as ACT, ICM and CTI, were found to be economically beneficial. In contrast, SCM did not offer good value for money compared to other interventions.

No economic evidence was found for peer support, injectable antipsychotics or substance use interventions.

What do the findings of this review mean?

PSH may improve and maintain housing stability. Further examination of implementation barriers of housing programmes is needed to inform decisionmakers.

Income assistance, SCM and intensive mental health interventions carry the potential to improve housing outcomes, but more research is needed to examine their mechanisms. Our results on mental health and other social outcomes were mixed and inconclusive. This could be attributed to the significant proportion of study participants who were suffering from chronic mental health or substance use conditions.

What are the implications for research and policy?

More longitudinal research is needed to better examine nonhousing outcomes. Furthermore, poor reporting, lack of blinding and allocation bias reduced the certainty and precision of our results.

There are other ongoing gaps that warrant more investigation, including peer support programmes, community substance use interventions, and programmes targeted towards special populations. Further examination of implementation barriers of housing programmes is also needed.

The absence of evidence on substance use interventions for people living with homelessness represents an important research and policy gap.

How up‐to‐date is this review?

The review authors searched for studies that had been published up until February 10, 2020.

BACKGROUND

The problem, condition or issue

Worldwide, over 1.8 billion people lack adequate housing and almost 25% of the world's urban population reside in informal accommodation (UN HRC, 2019). “People with a lived experience of homelessness” is a term coined to describe individuals who are, have been, or at risk of becoming homeless. This population lacks stable, permanent, appropriate housing, or may be without immediate prospect, means and ability to acquire it (Canadian Observatory on Homelessness, 2017). This population continues to grow, giving rise to a major international clinical and public health priority. Homelessness is strongly associated with high levels of morbidity (Hwang, 2009) and mortality (Nordentoft & Wandall‐Holm, 2003). People with lived experience of homelessness are at an increased risk for acute illnesses such as traumatic injury (including brain injury), frostbite, peripheral vascular disease, soft tissue infections, and dental decay (Hwang & Bugeja, 2000). Many homeless people also suffer from chronic medical conditions such as diabetes (Hwang & Bugeja, 2000), cardiovascular disease (Lee et al., 2005), cancer (Krakowsky et al., 2013) and respiratory illnesses (Raoult et al., 2001). Rates of serious mental illness (Fazel et al., 2014), cognitive impairment (Stergiopoulos et al., 2015b) and drug and alcohol use (Aubry et al., 2012; Grinman et al., 2010; Kennedy et al., 2017; Kerr et al., 2009; Torchalla et al., 2011) are disproportionately high, as are rates of homicide and suicide (Cheung & Hwang, 2004). Moreover, people who are homeless experience a disproportionately high prevalence of infectious diseases such as hepatitis C, HIV and tuberculosis (Beijer et al., 2012; Corneil et al., 2006; Roy et al., 2001). Despite the significant burden of disease, people with lived experience of homelessness are less likely to access and maintain the care required for their cure and treatment (Milloy et al., 2012; Palepu et al., 2011). People with lived experience of homelessness encounter many barriers to health and social care. The competing need to find food and shelter results in delays in accessing health care services (Gelberg et al., 1997) and those who do seek health care often experience discrimination that precludes adequate uptake of preventative health services (Wen et al., 2007). The structural stigma they experience when accessing health or social services is a major cause of their health inequities (Hatzenbuehler et al., 2013). For example, people with lived experience of homelessness with coexisting mental health conditions report specific barriers to accessing care, such as being unaware of the location of care, affordability, wait times and having experienced previous rejection from health or social services (Rosenheck et al., 1997). In addition, many health care recommendations, such as dietary advice, can prove impossible without access to resources, such as proper nutrition and cooking facilities (Hwang, 2001). This lack of appropriate access to community based care and reliable social contexts to implement preventive health behaviours results in disproportionately high acute care use by people with lived experience of homelessness (Saab et al., 2016). This population frequently experiences longer hospital stays and a higher risk of unplanned readmission than the general population (Saab et al., 2016), as discharge planning is compromised by inadequate housing to return to and suboptimal structures to support proper follow up care (Kushel, 2016).

Substantial research demonstrates that people with lived experience of homelessness benefit from receiving tailored, patient‐centred care within interprofessional teams with an integrated approach to community and social services (Coltman et al., 2015; Hwang & Burns 2014; James et al., 2005). A systematic review on health interventions for marginalised and socially excluded populations identified a range of potentially effective interventions that have relevance for marginalised and excluded populations, but it was not specific to people with lived experience of homelessness (Luchenski et al., 2017). Additionally, numerous studies have looked at the effectiveness of patient‐centred care for people with lived experience of homelessness within community services and social services (Coltman et al., 2015; Hwang & Burns 2014; James et al., 2005). Our review aims to evaluate current evidence on the effectiveness and cost effectiveness of interventions that directly or indirectly improve the health of those with lived experience of homelessness.

Description of the condition

The intervention

We evaluated the effectiveness and cost‐effectiveness of interventions for people with lived experience of homelessness that aim to improve these people's health, service usage, and social outcomes. Prior to conducting this systematic review, to rank the priority topics and the needs that were the most important for this vulnerable population, we used a Delphi Consensus process (Keeney et al., 2010) to engage 76 people with lived experience of homelessness and 84 healthcare workers and researchers with professional experience in the field of homelessness (Shoemaker et al., 2020). A literature review and consensus process informed the final selection of the five categories of interventions to be included in this review (see Figure 1).

Figure 1 Logic model (Figure not reproduced here; see the original article.)

Description of the intervention

Housing interventions

PSH is long‐term housing in the community combined with the provision of individualised supportive services that are tailored to participants' needs and choices. PSH follows the principles of “Housing First,” whereby the ability to access housing is not contingent on sobriety/abstinence, or the ability to follow through with treatment plans (Benston, 2015). This approach runs in contrast to what has been the orthodoxy of “treatment‐first” approaches, whereby people experiencing homelessness are placed in emergency services and must address certain personal issues (e.g., addictions, mental health) prior to being deemed “ready” for housing. Rather, in “Housing First,” the priority is to provide an individual with permanent housing and the choice to access treatment and supports, such as ACT or ICM offered by a multidisciplinary team (Aubry, Nelson, et al., 2015; Somers et al., 2017).

Income assistance interventions

Income assistance is a fundamental intervention for preventing and addressing homelessness. It consists of interventions that directly increase an individual's available income or improve their access to basic living necessities. Some examples include government assistance (i.e., income‐supplement programme (Brownell et al., 2016), charity donation or panhandling (Poremski et al., 2015), provision of cheques, tax benefits or cash transfers. Cash transfers are a form of financial aid offered on either a conditional or an unconditional basis (Lagarde et al., 2009). Further examples include support finding and maintaining employment or offering information on income benefits or financial literacy/debt‐management counselling (Abbott & Hobby, 2000), and the provision of food, daycare and fuel or rent supplements (Gruber et al., 2000; Power et al., 2015; Whittle et al., 2015).

SCM and peer support

Case management entails a myriad of services in which people with multiple morbidities or issues are supported by case managers who assess, plan and facilitate the access to health and social services that are necessary for the person's plan of care and recovery (De Vet et al., 2013). There are many different types of care‐coordination models, and these vary according to approach and caseload. The more intensive models of case management will be examined under “Mental‐health interventions”. Here, we will examine two specific areas of less intensive‐care coordination.

Standard case management

SCM allows for the coordination of an array of social, health‐care and other services to help individuals maintain good health and strong social relationships. This is achieved by “including engagement, assessment, planning, linkage with resources, consultation with families, collaboration with psychiatrists, patient psycho‐education, and crisis intervention” (Kanter, 1989). The Case Manager or navigator's role is performed by either a clinician, nurse, community outreach worker or social worker with an average caseload of 35 clients (De Vet, 2013; Guarino, 2011). The target population for standard case‐management models are people who are experiencing homelessness or those who are vulnerably‐housed and have complex health concerns and are presenting to primary‐care practitioners and are often provided with this type of care as a time‐limited service (De Vet, 2013).

Peer support

Peer support includes the sharing of knowledge, experience, emotional, social or practical help by or with an individual who has experienced a similar background to the service user (Mead et al., 2001). Peer support workers may be termed differently in different settings, either as mentors, recovery coaches, or life coaches, and all offer emotional and social support to individuals who are newly homeless or on a treatment plan or path to recovery from substance use or homelessness (Barker & Maguire, 2017). Thus, due to their shared experiences and ability to establish a relationship built on trust, peers are uniquely positioned to assist persons experiencing homelessness due to their shared experiences and ability to establish a relationship built on trust (Barker & Maguire, 2017; Faulkner & Basset, 2012; Finlayson et al., 2016).

Mental health interventions

We assessed four evidence‐supported interventions that are relevant to serious mental illness, which is defined as conditions that substantially limit major life activities due to functional impairment (SAMHSA, 2016).

Assertive community treatment

ACT consists of a multidisciplinary group of healthcare workers in the community, that offers team‐based care to persons with high levels of needs. This team has 24‐h/day, 7‐days/week availability and provides services tailored to the needs and goals of each service user (Coldwell & Bender, 2007; De Vet et al., 2013). There is no time limit on the services provided, but transfer to lower intensity services is common after a period of stability (Homeless Hub, n.d.) Ten service users per case manager is the typical caseload, and services are offered in a natural setting, such as the workplace, home or social setting (De Vet et al., 2013).

Intensive case management

ICM is offered to persons with serious mental illness but who typically have moderate needs, such as fewer hospitalisations or less functional impairment, as well as for people experiencing addictions (Dieterich et al., 2017). ICM helps service users through the support of a case manager that brokers access to an array of services. The case manager accompanies the service user to meetings and can be available for up to 12 h/day, 7 days a week. Case managers for ICM often have caseloads of 15–20 service users each (De Vet, 2013).

Critical time intervention

CTIs are a form of time‐limited ICM, defined as a service that supports continuity of care for service users during times of transition; for example, from a shelter to independent housing or following discharge from the hospital. This service strengthens the person's network of support in the community (Silberman School of Social Work, 2017). It is administered by a CTI worker and is usually limited to a period of 6–9 months after institutional discharge or placement in housing. It comprises of three phases: Phase 1: Transition—Provide support and begin to connect the client to people and agencies that will assume the primary role of support; Phase 2: Tryout—Monitor and strengthen support network and client's skills; Phase 3: Transfer of care—Terminate CTI services with support network safely in place (Gaetz et al., 2013; Herman & Mandiberg, 2010).

Injectable antipsychotics

Injectable antipsychotics have a major role to play in the treatment for psychosis of patients living in precarious situations as these individuals often have a limited ability to follow through with oral medication treatment plans (Llorca et al., 2013). The clinical effectiveness of newer (aripiprazole, olanzapine, paliperidone and risperidone) and older antipsychotics (haloperidol, fluphenazine, flupenthixol) is similar (Castillo & Stroup, 2015), but their effectiveness among homeless and vulnerably housed persons is unknown.

Interventions for substance use

We assessed three interventions relating to substance‐use disorders (SUDs) that apply to people experiencing homelessness and those who are vulnerably housed.

Supervised consumption facilities (SCFs)

SCFs are legally sanctioned facilities where people who use substances can consume pre‐obtained substances under supervision (Drug Policy Alliance, n.d.). There exist various terminologies for these facilities, including supervised injection facilities (SIF), supervised consumption sites (SCS), medically supervised injection centres (MCIS), among others. Such facilities are frequently used as safe spaces for people experiencing homelessness and those who are vulnerably housed as well as substance users.

Managed alcohol programmes

A MAP provides shelter, medical assistance, social services and the provision of regulated alcohol to help residents cope with severe alcohol use disorder (Shepherds of Good Hope Foundation, n.d.). This programme is provided by professional staff and nurses.

Pharmacological interventions for opioid use disorder

The effectiveness and cost‐effectiveness of opioid therapy medications, including buprenorphine/naloxone, naloxone, naltrexone (British Columbia Centre on Substance Use, 2017) methadone, and injectable diacetylmorphine (heroin; Haasen et al., 2007), have been documented in general‐population studies. The literature demonstrates the effectiveness of naltrexone (Krupitsky et al., 2011), buprenorphine (with or without naloxone), and methadone (McKeganey et al., 2013), as well as injectable diacetylmorphine (heroin; Haasen et al., 2007) for treating opiate dependence, but the evidence specific to homeless populations is yet to be synthesised.

How the intervention might work

Housing interventions

Access to adequate housing is an end‐all objective of most homeless individuals. The unconditional provision of stable housing that is permanent in tenure, supportive in nature, and scattered across the rental market has been associated with a positive impact on the long‐term residential stability of homeless individuals (Aubry et al., 2016; Tsemberis et al., 2004). As well, synchronising the provision of permanent housing with supportive services is found to improve social functioning and quality of life (Aubry et al., 2016; Stergiopoulos et al., 2015).Another model of providing PSH is to congregate accommodation units with supportive services in a single location that may be situated in a residential or commercial area and equipped with commonly used facilities. Such models were found to positively improve the housing and health‐related outcomes of homeless individuals, as per the scattered model (Somers et al., 2017).

Income assistance interventions

Financial hardships halt all efforts to end the cycle of homelessness (Institute of Medicine (US) Committee on Health Care for Homeless People, 1988). Evidence suggests that increasing income is an effective strategy to improve both access to health services and health status (Lagarde et al., 2009). This correlation may, very well, be the result of reduced financial stressors and increased ability to afford fundamental life necessities, such as housing, food, and medications (Richards et al., 2008). Moreover, it was found that providing information on income‐assistance resources has the potential to improve the physical and psychosocial health of disadvantaged populations (Adams et al., 2006).

SCM and peer support

Standard case management

Regardless of the heterogeneity and complexity of case‐management models, literature suggests that case management is associated with improved residential stability and substance‐use outcomes (De Vet, 2013). Patients who are provided with the services of a case manager are more likely to feel supported and guided in their quest to access and maintain fundamental health and social services (Conrad et al., 1998).

Peer support

The peer‐support model employs workers with shared life experiences to provide social support, advocacy, education, and role modelling to homeless individuals (Barker & Maguire, 2017). Among homeless populations, these elements have been found to improve quality of life and reduce problematic substance use (Barker & Maguire, 2017).

Mental health interventions

Assertive community treatment

Evidence suggests that individuals experiencing homelessness may benefit from receiving support in the form of ACT. This model of care is found to reduce days on the street or hospitalised, increase community functioning, and improve life satisfaction and mental‐health‐related outcomes for this vulnerable population (Coldwell & Bender, 2007; De Vet, 2013). The positive impact of this model of care could be attributed to the strength of the provider‐service‐user relationship and the sincere effort of the multidisciplinary team providing the care (Stuart, 2009).

Intensive case management

Literature is abundant with evidence that suggests the added benefits of providing ICM to disadvantaged populations. This model of care carries the potential to decrease hospitalisations, increase access to care and reduce economic hardships (De Vet, 2013; Dieterich et al., 2017).

Critical time intervention

The benefit of CTI lies in its ability to prevent the discontinuity of care during periods of transition. Providing CTI to homeless individuals was associated with increased residential stability, decreased mental‐health symptomatology and strengthened ties with services, family, and friends (De Vet, 2013; Jones et al., 2003).

Injectable antipsychotics

Injectable antipsychotics have been found to be effective for managing serious mental illnesses and reducing episodes of mental‐health emergencies (Llorca et al., 2013).

Interventions for substance use

Supervised consumption facilities

There is increasing evidence suggesting the benefit of SCFs in reducing precarious substance‐use‐related public behaviours and increasing access to and maintenance of treatment services (Kennedy et al., 2017; Wood et al., 2007). These facilities are believed to provide a safe environment for accessible services that provide nonjudgemental staff who help connect clients to health and social services as needed.

Managed alcohol programmes

MAPs follow a harm‐reduction approach by providing clients with shelter and regulated alcohol dispensing, accompanied by health and social support as needed (Podymow et al., 2006). The scarce literature on these interventions among homeless individuals suggest its effectiveness in reducing alcohol intake, hospitalisations and incarcerations (Podymow et al., 2006).

Pharmacological interventions for opioid use disorder

Opioid agonist therapy (OAT) such as methadone, buprenorphine/naloxone, and oral morphines have been associated with decreased mortality and morbidity (British Columbia Centre on Substance Use, 2017). As well, evidence suggests that opioid antagonist therapy such as naltrexone is successful in mitigating overdose‐related mortalities and incarceration rates (Roozen et al., 2006).

Why it is important to do this review

There has been a long‐standing social discourse on effectively tackling the negative consequences of the urban homelessness that has plagued communities internationally. Persons with lived experience of homelessness face higher rates of infectious and chronic disease and disproportionately poorer outcomes, with reduced rates of access to effective quality care. In order to better understand the needs and resources available for people with lived experience of homelessness, policymakers, practitioners, and allied health professionals need high‐quality systematic reviews and knowledge‐translation strategies on interventions that are specific to this population. Our review aims to provide a comprehensive overview of the benefits and cost‐effectiveness of interventions designed to indirectly or directly improve the health and well‐being of persons with lived experience with homelessness. We present updated perspectives on the effect of PSH, income assistance, SCM/peer support and mental‐health and substance‐use interventions, on the housing stability, mental health, quality of life, hospitalisations, earned income and employment statuses of persons with lived homelessness. This review is part of a series of other publications that inform a national practice guide on homelessness (Pottie et al., 2020), and serves to provide best‐practice updates to health‐care professionals and policymakers and guide the future care of persons with lived experiences of homelessness.

OBJECTIVES

The objective of this systematic review is to identify, appraise, and synthesise the best available evidence on the effectiveness and cost‐effectiveness of interventions to improve the health and social outcomes of people experiencing homelessness and those who are vulnerably housed. Our outcomes of interest include housing stability, mental health, quality of life, substance use, hospitalisations, employment and income. The following research questions were developed to guide the formation of the systematic review:1.What is the effectiveness of PSH on the health and social outcomes of people experiencing homelessness and those who are vulnerably housed?2.What is the effectiveness of income assistance on the health and social outcomes of people experiencing homelessness and those who are vulnerably housed?3.What is the effectiveness of SCM and/or peer support on the health and social outcomes of people experiencing homelessness and those who are vulnerably housed?4.What is the effectiveness of mental‐health interventions (ACT, ICM, CTI and injectable antipsychotics) on the health and social outcomes of people experiencing homelessness and those who are vulnerably housed?5.What is the effectiveness of interventions for substance use (SCFs, MAPs and pharmacological interventions for opioid use disorder) on the health and social outcomes of people experiencing homelessness and those who are vulnerably housed?6.What are the costs and cost‐effectiveness of the aforementioned interventions for people experiencing homelessness and those who are vulnerably housed?

METHODS

Criteria for considering studies for this review

Types of studies

The protocol was registered with the Campbell Collaboration (Pottie et al., 2019) and reported according to the preferred reporting items for systematic reviews and meta‐analyses for protocols (PRISMA‐P; Moher et al., 2015). The results of the review are reported using the PRISMA reporting guidelines (Moher et al., 2009).

We included studies as recommended by the Cochrane Effective Practice and Organisation of Care (EPOC) Cochrane group for reviews of effectiveness (Effective Practice and Organisation of Care (EPOC)‐Cochrane, 2015). We included randomised control trials (RCTs), non‐RCTs, controlled before‐after studies, interrupted time‐series studies, and repeated‐measures studies. We considered studies published in both peer‐reviewed journals and grey literature.

Types of participants

We included populations experiencing homelessness, defined as those who lack stable, permanent, appropriate housing, or who may be without immediate prospects, means, and ability to acquire it. Such physical living situations can include emergency shelters or provisional accommodations (Canadian Definition of Homelessness, 2017). Studies must have reported whether participants were experiencing homelessness in order to be included in this review. We included studies that included a subset of the sample experiencing homelessness as long as 50% of the participants were homeless. We included studies that were among individuals or families and we did not restrict our inclusion criteria by age, sex or gender. We excluded studies that were specific to indigenous populations experiencing homelessness, as this line of inquiry is being pursued by an indigenous‐specific research team (Thistle & Smylie, 2020). We excluded all other populations.

Types of interventions

We included the following interventions, as outlined in Section 1.1.2: PSH: income assistance, SCM, ICM, ACT, CTI, peer support, SCFs, MAPs, injectable antipsychotics, and OAT. We included studies that had multicomponent interventions as long as one of the interventions applied to those mentioned above.

All of the included interventions were either compared to an inactive control (i.e., a placebo, no treatment, standard care) or to an active control intervention (alternative or variant of the intervention; Effective Practice and Organisation of Care (EPOC)‐Cochrane, 2015). In the case of an interrupted time series, the control must have been a historical control with three data points. If a study with more than two intervention arms was included, then we only included the intervention and control arms that met the eligibility criteria.

Types of outcome measures

Studies were included in this review if they reported the use of validated measures and reported at least one of the following outcomes.

Primary outcomes

1.Housing stability: Any measures assessing participants housing status, such as the number of days in stable housing, number of days homeless (on the street or in shelters), number of participants in stable housing, and number of participants homeless (on the street or in shelters). Typical tools to measure housing stability include the Residential Timeline Followback Inventory (RTLFB) (Tsemberis et al., 2007).

Secondary outcomes

2.Mental health: any measures assessing psychological status and wellbeing, including but not limited to, psychological distress, self‐reported mental health status, or mental illness symptoms. Typical tools to measure mental health include the Colorado Symptom Index (CSI) (Boothroyd & Chen, 2008), and the self reported mental status SF‐12 (Nelson et al., 2012).3.Quality of life: which include any assessment of well‐being, life and personal satisfaction, quality of social relationships, and any specific physical or mental quality of life measures. Typical tools to measure quality of life include the Lehman Quality of Life Interview (Lehman et al., 1996), and the EuroQoL 5‐D scale (Lamers et al., 2006).4.Hospitalisation: any measures of participants' use of hospital and emergency services, such as the number of days hospitalised or number of visits to the emergency department. Such measures can be assessed through a standard questionnaire asking participants for their service use, or through accessing the hospital data sets.5.Substance use: As measured by the number of days using alcohol or substance, the rate and frequency of using alcohol or substances, number of days of abstinence from alcohol or substances or physical and mental consequences of using alcohol or substances. Typical tools to measure substance use outcomes include the Global Appraisal of Individual Needs‐Short Screener of Substance Use Problems GAIN‐SS (Dennis et al., 2006).6.Income: Any measures of money that participants acquire from different resources including social assistance, disability benefits, donations, and part or full time employment. Such measures can be assessed through a standard questionnaire asking participants for their weekly, monthly or annual income from different sources.7.Employment: Any measures of employment that participants partake during the study period, including but not limited to, number of days of paid employment, number of employed or unemployed participants, hourly wage, and employment tenure. Such measures can be assessed through a standard questionnaire asking participants about their employment rates during the study period.8.Economic outcome: any measures of cost, cost benefit, cost utility or incremental cost‐effectiveness ratio. Such measures can be obtained from administrative databases and cost reports. An example of how an individualised programme cost could be calculated is dividing the sum of all on‐site operation and services costs (maintenance, utilities, insurance, etc.) by the capacity of the project (Larimer, 2009).

Duration of follow‐up

All durations of follow‐up were included. We collected data at each available time‐point.

Types of settings

We included studies where the intervention took place in any setting where the primary care of people experiencing homelessness takes place. Primary care is known as the “entry point to the larger health care system” (Tarlier, 2007) and can be provided by professionals from many disciplines, such as family physicians, psychiatrists, social workers, emergency physicians, and so forth. We also included community‐based interventions provided in social‐service or shelter/supervised consumption locations, private or nonprivate clinics, hospital emergency rooms, outreach care, street patrols, mobile care units, and so forth.

We included studies that occurred in high‐income countries and excluded studies that occurred in low‐ and middle‐income countries (World Bank, 2019).

Search methods for identification of studies

We searched for relevant literature in consultation with an information specialist (librarian).

Electronic searches

We searched the following bibliographic databases from database inception to February 10, 2020:Ovid MEDLINE(R) and Epub Ahead of Print, In‐Process & Other Non‐Indexed Citations, Daily and Versions(R) (1946 to February 7, 2020)EBM Reviews—Cochrane Central Register of Controlled Trials (January 2020)EBM Reviews—Cochrane Database of Systematic Reviews (2005 to February 4, 2020)EBM Reviews—Database of Abstracts of Reviews of Effects (1st Quarter 2016)EBM Reviews—Health Technology Assessment (4th Quarter 2016),EBM Reviews—NHS Economic Evaluation Database (1st Quarter 2016)Embase (1974 to February 7, 2020)EBSCO CINAHL (–2020)EBSCO PsycINFO (–2020)Epistemonikos (–2020)

We used a combination of subject headings and keywords including “homeless”, “marginalized” and “shelter”. Full strategies for each database can be found in Appendix A.

Searching other resources

The reference lists of all articles selected for full‐text review were manually searched for relevant citations. These were cross‐referenced against our original search results and any additional potentially relevant citations were screened. Further, we consulted content experts for any publications or resources that might enrich our findings and we screened their suggestions against our inclusion criteria.

Data collection and analysis

We collected and analysed data according to our protocol (Pottie et al., 2019).

Selection of studies

Teams of two reviewers independently screened titles and abstracts in duplicate. We pilot tested the screening criteria at both the title‐and‐abstract‐screening stage and the full‐text stage. We used the PRISMA flow diagram to report the eligibility of studies. We retrieved the full text of all of the studies that passed this first‐level screening. The full‐text reviews were also done in duplicate by two reviewers, and agreement was reached by consensus. Disagreements were resolved by consultation with a third reviewer.

Data extraction and management

We developed a standardised extraction sheet for each topic variable and created a table of characteristics to describe a summary of findings from our included studies. The data extraction sheet was piloted by two independent reviewers. We collected and utilised all relevant numerical data (SDs, effects estimates, confidence intervals [CIs], test statistics, p values, etc.). Teams of two reviewers extracted data in duplicate and independently. The reviewers compared their results and resolved disagreements by discussion or with help from a third reviewer.

Assessment of risk of bias in included studies

We assessed risk of bias according to guidance for Cochrane Effective Practice and Organisation of Care (EPOC) reviews (Effective Practice and Organisation of Care (EPOC)‐Cochrane, 2015). Nine standard criteria are suggested for all randomised trials, nonrandomised trials and controlled before‐after studies, including random‐sequence generation, allocation concealment, baseline‐outcome measurements, baseline characteristics, incomplete‐outcome data, knowledge of the allocated interventions adequately prevented during the study, protection against contamination, selective outcome reporting, and other biases.

Risk of bias was assessed by teams of two review authors, in duplicate. Discrepancies were resolved through discussion or by a third reviewer.

It is important to highlight that we did not subject any of the identified economic evaluations to critical appraisal, in accordance with guidance from the Cochrane Handbook (Shemilt et al., 2019).

Measures of treatment effect

Whenever possible, we performed statistical analyses using RevMan 5. For dichotomous data, we used odds ratios (OR) and risk ratios (RR) with 95% CIs. For continuous data, we used the mean difference (MD) with 95% CI, if the outcomes were measured in the same way between trials. We used the standardised mean difference (SMD) with 95% CI to combine the trials that measured the same outcome but used different methods of measurement.

Unit of analysis issues

The results from some studies were reported in multiple publications. Therefore, to prevent the double counting of data, individual records were screened to identify unique studies and were evaluated for potential overlap by comparing the study design, enrolment and data‐collection dates, authors and their associated affiliations, and the reported selection and eligibility criteria. When reviewing multiple publications, we included only unique data from each study. Several studies included outcome data for multiple time points. Comparisons were therefore carried out separately for periods of 6 months and less (short term), 6–18 months (midterm), and 18 months or more (long‐term). If multiple measures of the same outcome were reported, we prioritised outcomes measured using validated scales for meta‐analyses and reported all available outcome data narratively.

Dealing with missing data

We will contact authors once for any missing data. We will use any supplementary data provided by authors in our analysis, or report findings as extracted otherwise.

Assessment of heterogeneity

We assessed heterogeneity among studies in two ways. First, we assessed clinical heterogeneity: heterogeneity in population, interventions or outcomes. We used I ² statistics as a guide to assess heterogeneity along with a visual inspection of forest plots.

Assessment of reporting biases

There were very few outcomes that provided enough data for a meta‐analysis; therefore we could not assess for reporting bias. For future updates, funnel plots would be used if there are 10 or more studies in a meta analysis for one outcome and an investigation would be conducted for reporting biases, for example, publication bias.

Data synthesis

We aimed to conduct a separate meta‐analysis for each outcome and intervention. We assessed clinical heterogeneity by considering the study population, intervention, comparison, outcome measure, and timing of outcome assessment. The assessments were made in consultation with members of the research team with clinical and statistical expertise. We pooled data from studies we judged to be clinically homogeneous. If more than one study provided usable data in any single comparison, we performed a meta‐analysis. We standardised all the reported effect sizes as RRs for the dichotomous outcomes and MDs or SMDs for the continuous outcomes. For the majority of findings, characteristics of studies (such as study designs, intervention types, or outcomes) were too diverse to yield a meaningful summary estimate of effect. Similarly, we deemed forest plots of single studies to be of limited value to the review. When heterogeneity precluded a meta analysis, we synthesised our findings narratively as recommended by the synthesis without meta‐analysis (SWiM) reporting guideline (Campbell et al., 2020).

Subgroup analysis and investigation of heterogeneity

Based on the availability of the data, we had planned to conduct subgroup analyses for the following subgroups: women, youth, and people with disabilities. However, since very few studies were included in each comparison within the review, we could not conduct any of the aforementioned subgroup analyses.

Sensitivity analysis

We had planned to conduct sensitivity analyses; however, since very few studies for each intervention were included in the review, we could not conduct any sensitivity analyses.

Summary of findings and assessment of the certainty of the evidence

We assessed the certainty of evidence for housing‐stability outcomes by using the GRADE (Grading of Recommendations, Assessment, Development and Evaluations) approach (Balshem et al., 2011). Housing‐stability outcomes were selected as critical patient‐important outcomes by our review team, in consultation with content experts and people with lived experience of homelessness. GRADE rates certainty of evidence are as follows:

RESULTS

Description of studies

We included 86 studies, described below.

Results of the search

The search was performed from database inception up to February 10, 2020. The search resulted in 15,889 citations, and an additional 33 were identified from other sources. After removal of duplicates we screened 10,117 unique citations by title and abstract, leaving 353 citations that were potentially eligible for inclusion in this review. Full‐text reviews of these works identified 128 citations for inclusion in this review. Figure 2 depicts the search‐and‐selection flow diagram.

Figure 2 PRISMA flow diagram (Figure not reproduced here; see the original article.)

Included studies

We included a total of 86 studies (128 publications), broken down by the interventions below:

Permanent supportive housing

We included 15 studies (41 publications) examining the effectiveness of PSH (Aubry et al., 2016; Cherner et al., 2017; Goldfinger et al., 1999; Hwang et al., 2011; Lipton et al., 1988; Martinez & Burt, 2006; McHugo et al., 2004; Rich & Clark, 2005; Sadowski et al., 2009; Siegel et al., 2006; Stefancic & Tsemberis, 2007; Stergiopoulos et al., 2015; Stergiopoulos et al., 2019; Tsemberis et al., 2004; Young et al., 2009). Four studies were conducted in Canada (Aubry et al., 2016; Cherner et al., 2017; Hwang et al., 2011; Stergiopoulos et al., 2019) and the remaining were conducted in the United States. All studies provided PSH with either ACT or ICM, depending on the severity of the mental‐health symptoms and participants' needs. PSH models included scattered‐site and congregate settings. All interventions were delivered to individuals and no studies were specific to families, women or youth.

Income assistance

We included 10 studies (15 publications) examining the effectiveness of income‐assistance interventions (Booshehri, 2017; Ferguson, 2018; Forchuk et al., 2008; Gubits et al., 2018; Hurlburt et al., 1996; Kashner, 2002; Pankratz et al., 2017; Poremski et al., 2015; Rosenheck et al., 2003; Wolitski, 2009). Five studies investigated the impact of housing subsidies with (Hurlburt et al., 1996; Pankratz et al., 2017; Rosenheck et al., 2003; Wolitski, 2009) or without (Gubits et al., 2018) case management. One study offered assistance finding housing and rental supplements (Forchuk et al., 2008) and the remaining four studies assessed the effectiveness of financial education (Booshehri, 2017), compensated work therapy (CWT; Kashner, 2002), or individual‐placement support (IPS; Ferguson, 2018; Poremski et al., 2015). Two studies were conducted among families (Booshehri, 2017; Gubits et al., 2018) and one among youth (Ferguson, 2018). Three studies were conducted in Canada (Forchuk et al., 2008; Pankratz et al., 2017; Poremski et al., 2015) and the remaining seven took place in the United States.

Standard case management

We included 10 studies (11 publications) examining the effectiveness of SCM (Conrad et al., 1998; Graham‐Jones et al., 2004; Hurlburt et al., 1996; Lapham et al., 1996; Nyamathi et al., 2001; Nyamathi et al., 2016; Sosin et al., 1995; Towe et al., 2019; Upshur et al., 2015; Weinreb et al., 2016). All studies were conducted among populations either experiencing or at‐risk for homelessness, with varying degrees of need. Three studies were specific to women (Nyamathi et al., 2001; Upshur et al., 2015; Weinreb et al., 2016); two were specific to men (Conrad et al., 1998; Nyamathi et al., 2016), and five contained mixed‐gender populations (Graham‐Jones et al., 2004; Hurlburt et al., 1996; Lapham et al., 1996; Sosin et al., 1995; Towe et al., 2019). Most (n = 9) studies were set in the United States and one study was conducted in the United Kingdom (Graham‐Jones et al., 2004). The interventions focused on care coordination, including links to primary care (Graham‐Jones et al., 2004; Nyamathi et al., 2001; Weinreb et al., 2016), housing (Hurlburt et al., 1996; Sosin et al., 1995), mental‐health counselling (Lapham et al., 1996; Upshur et al., 2015), and skills provision, such as relapse prevention skills (Conrad et al., 1998), infectious‐disease risk reduction (Nyamathi et al., 2001), and coping skills (Nyamathi et al., 2016). Two studies also included peers with lived experience in their intervention delivery (Nyamathi et al., 2001; Nyamathi et al., 2016).

Peer support

We included six studies (six publications) examining the effectiveness of peer‐support interventions (Corrigan et al., 2017; Ellison et al., 2020; Lapham et al., 1996; Nyamathi et al., 2001; Nyamathi et al., 2016; Yoon et al., 2017). Of these, three studies were three‐arm trials where the third arm is also included under SCM (Lapham et al., 1996; Nyamathi et al., 2001; Nyamathi et al., 2016). All studies were conducted in the United States. In four studies, peers played the role of navigators and mentors, providing training in effective coping skills, self‐management, goal‐setting and assistance in navigating the health‐care and social‐care systems (Corrigan et al., 2017; Nyamathi et al., 2001; Nyamathi et al., 2016; Yoon et al., 2017). Two studies integrated peers into housing programmes, where peers offered support services focused on mental health and substance‐use recovery and community integration (Ellison et al., 2020; Lapham et al., 1996).

Intensive case management

We included 16 studies (17 publications) examining the effectiveness of ICM (Braucht, 1995; Burnam, 1995; Cauce, 1994; Clark & Rich, 2003; Cox et al., 1998; Felton et al., 1995; Grace & Gill, 2014; Korr & Joseph, 1996; Malte et al., 2017; Marshall et al., 1995; Orwin et al., 1994; Rosenblum et al., 2002; Shern et al., 2000; Shumway et al., 2008; Stahler et al., 1995; Toro et al., 1997). Most studies were conducted among homeless individuals with mental illness and/or substance‐use problems, with two studies conducted among adolescents and young adults (Cauce, 1994; Grace & Gill, 2014) and one conducted among adults with children (Toro et al., 1997). Fourteen studies were conducted in the United States, one study was conducted in the United Kingdom (Marshall et al., 1995) and one in Australia (Grace & Gill, 2014). All interventions had a low caseload (12–20 clients) and one intervention included peers with lived experience (Felton et al., 1995).

Assertive community treatment

We included 8 studies (10 publications) examining the effectiveness of ACT (Clarke et al., 2000; Essock et al., 1998, 2006; Fletcher et al., 2008; Lehman et al., 1997; Morse et al., 1992, 1997, 2006). All studies were conducted among homeless adults, in the United States, who had serious and persistent mental illness. All participants received care from a multidisciplinary team that included a psychiatrist. Two studies also integrated a substance‐abuse specialist to their staff (termed “Integrated Assertive Community Treatment” [IACT]) (Fletcher et al., 2008; Morse et al., 2006). Three studies also included peers with lived experience of homelessness and/or poor mental health (often termed “consumers”, “consumer advocates” or “community workers”) in their ACT teams (Clark et al., 1998; Lehman et al., 1997; Morse et al., 1997).

Critical time intervention

We included five studies (11 citations) examining the effectiveness of CTI (De Vet et al., 2017; Herman et al., 2011; Lako et al., 2018; Shinn et al., 2015; Susser et al., 1997). Four studies were conducted among single adults and one study was conducted among families with children (Shinn et al., 2015). One study was conducted following participants' hospital discharge (Herman et al., 2011) and the remaining four studies were conducted while participants were residing in shelters. Two studies were conducted in the Netherlands (De Vet, 2017; Lako et al., 2018) and the other three were conducted in the United States. All CTI interventions followed the same three phases: (1) transition to the community, (2) tryout and (3) transfer of care.

Supervised consumption facilities

We did not identify any eligible studies on SCFs (empty review).

Managed alcohol programmes

We did not identify any eligible studies on MAPs (empty review).

Injectable antipsychotics

We did not identify any eligible studies on injectable antipsychotics (empty review).

Opioid agonist therapy

We did not identify any eligible studies on OATs (empty review).

Cost‐effectiveness

We identified 30 publications that reported on the cost‐effectiveness of our interventions (Aubry et al., 2016; Chalmers McLaughlin, 2011; Clark et al., 1998; Culhane et al., 2002; Dickey et al., 1997; Essock et al., 1998; Evans et al., 2016; Gilmer et al., 2009, 2010; Holtgrave et al., 2013; Hunter et al., 2017; Larimer, 2009; Latimer et al., 2019; Lehman, 1999; Lenz‐Rashid, 2017; Lim et al., 2018; Mares & Rosenheck, 2011; Morse et al., 2006; Nyamathi et al., 2016; Okin et al., 2000; Pauley et al., 2016; Rosenheck et al., 2003; Sadowski et al., 2009; Schinka et al., 1998; Shumway et al., 2008; Srebnik et al., 2013; Stergiopoulos et al., 2015; Susser et al., 1997; Tsemberis et al., 2004; Wolff, 1997). Of these, 10 publications were also included as part of the effectiveness data (Aubry et al., 2016; Essock et al., 1998; Morse et al., 2006; Nyamathi et al., 2016; Rosenheck et al., 2003; Sadowski et al., 2009; Shumway et al., 2008; Stergiopoulos et al., 2015; Susser et al., 1997; Tsemberis et al., 2004). Thus, the cost‐effectiveness analysis includes an additional 19 studies (20 publications). Eighteen of these studies took place in the United States, and only one examined cost‐effectiveness in the Canadian context (Latimer et al., 2019).

Twenty‐one publications provided cost‐effectiveness data on PSH and/or income‐assistance interventions (Aubry et al., 2016; Chalmers McLaughlin, 2011; Culhane et al., 2002; Dickey et al., 1997; Evans et al., 2016; Gilmer et al., 2009, 2010; Holtgrave et al., 2013; Hunter et al., 2017; Larimer, 2009; Latimer et al., 2019; Lenz‐Rashid, 2017; Lim et al., 2018; Mares & Rosenheck, 2011; Pauley et al., 2016; Rosenheck et al., 2003; Sadowski et al., 2009; Schinka et al., 1998; Srebnik et al., 2013; Stergiopoulos et al., 2015; Tsemberis et al., 2004). Of these, five publications also provided effectiveness data (Aubry et al., 2016; Rosenheck et al., 2003; Sadowski et al., 2009; Stergiopoulos et al., 2015; Tsemberis et al., 2004).

For mental‐health interventions, twelve articles provided evidence on cost‐effectiveness: three on SCM (Nyamathi et al., 2016; Okin et al., 2000; Shumway et al., 2008), 6 on ACT (Aubry et al., 2016; Clark et al., 1998; Essock et al., 1998; Lehman, 1999; Morse et al., 2006; Wolff, 1997), 2 on ICM (Rosenheck et al., 2003; Stergiopoulos et al., 2015); and 1 for CTI (Susser et al., 1997). Eight of the mental‐health cost‐effectiveness articles were also included in the effectiveness analysis (Aubry et al., 2016; Essock et al., 1998; Nyamathi et al., 2016; Morse et al., 2006; Rosenheck et al., 2003; Shumway et al., 2008; Stergiopoulos et al., 2015; Susser et al., 1997).

No cost‐effectiveness studies were identified for the other interventions (peer support, SCFs, MAPs, injectable antipsychotics and OAT).

Excluded studies

The search process is diagrammed in Figure 2, which also shows the number of records excluded (n = 225), along with a summary of reasons. Further details of the excluded studies are also available in Excluded studies.

Risk of bias in included studies

We judged there to be a moderate or high risk of bias in most categories in each of the studies reviewed, see Figure 3 for a summary of judgements on bias across the studies reviewed. Figure 4 provides an insight into the level of potential bias within each study. Characteristics of included studies provides the rationale for each of these judgements. Furthermore, given that the risk of bias associated with economic evaluations differs from that associated with standard RCTs, we did not critically appraise these studies using a standardised tool.

Figure 3 Risk of bias summary (Figure not reproduced here; see the original article.)

Figure 4 Risk of bias in individual studies (Figure not reproduced here; see the original article.)

Allocation (selection bias)

Selection bias occurs in intervention studies when there are systematic differences between comparison groups in response to treatment or prognosis (Henderson & Page, 2007). Intervention studies are especially susceptible to selection bias unless particular efforts are made to minimise it. The most effective method is random allocation to treatment and control groups. We included both randomised and nonrandomised trials of interventions in our review. As a result, 15 studies were assessed as having high risk of selection bias due to inadequate or absent random sequence generation, while 28 studies had unclear risk of bias on this item. Concerns with allocation concealment were similar, with only 14 deemed as low risk of bias.

Blinding (performance bias and detection bias)

This potential bias is counteracted by the blinding of study participants and personnel, so that they are unaware of their group assignment, and the blinding of outcome assessors. Given the nature of the interventions and the impossibility of blinding of participants, all studies were assessed as high risk for performance bias. Blinding of outcome assessors was often poorly described in our included studies, resulting in the majority of studies having unclear risk of detection bias. Eleven studies did not blind their outcome assessors (assessed as high risk of bias), resulting in only eight studies having low risk of detection bias.

Incomplete outcome data (attrition bias)

Attrition bias refers to the biasing effect of study participants, or study participant data becoming unavailable during the study. This bias can be counteracted by keeping accurate records of participants who drop out of the study, and by using intention‐to‐treat analysis so that drop‐outs do not have a biasing effect on final results. Nineteen studies had high risk for attrition bias, while 11 studies had unclear risk of bias on this item.

Selective reporting (reporting bias)

This bias refers to the selection of a subset of the original recorded outcomes, on the basis of the results, for inclusion in publication. Evidence of this bias was assessed by examining studies for an existing protocol. Among included studies, only four studies had high risk of bias on this item.

Other potential sources of bias

We considered publication bias and funding source bias as other potential sources of bias. Seventeen studies had unclear or high risk of the presence of these other biases.

Effects of interventions

Permanent supportive housing

Primary outcome: Housing stability

The effect of PSH on housing stability was examined in 15 studies (41 citations) (Aubry et al., 2016; Cherner et al., 2017; Goldfinger et al., 1999; Hwang et al., 2011; Lipton et al., 1988; Martinez & Burt, 2006; McHugo et al., 2004; Rich & Clark, 2005; Sadowski et al., 2009; Siegel et al., 2006; Stefancic & Tsemberis, 2007; Stergiopoulos et al., 2015; Stergiopoulos et al., 2019; Tsemberis et al., 2004; Young et al., 2009). Ten studies were from the United States (Goldfinger et al., 1999; Lipton et al., 1988; Martinez & Burt, 2006; McHugo et al., 2004; Rich & Clark, 2005; Sadowski et al., 2009; Siegel et al., 2006; Stefancic & Tsemberis, 2007; Tsemberis et al., 2004; Young et al., 2009) and 5 were from Canada (Aubry et al., 2016; Cherner et al., 2017; Hwang et al., 2011; Stergiopoulos et al., 2015; Stergiopoulos et al., 2019). Between the 15 studies, follow‐up ranged from 6 months to up to 6 years. Eight studies were RCTs, 1 was an extension of a multicentre RCT, 5 were quasi‐experimental trials and 1 was a controlled before‐and‐after study. Almost all trials included mental illness within the study's inclusion criteria, and many participants also had comorbid substance‐abuse disorders. Due to heterogeneity in the outcome measures and the time points measured, it was not possible to complete a meta‐analysis of all of the studies. However, data analysis from the Canadian At‐Home Chez‐Toi and US Pathways trials were pooled and is presented in Analysis 1.1 (see Figure 5).

Figure 5 (Analysis 1.1) Figure 3. Forest plot of meta‐analysis comparing PSH to TAU on number of days in stable at 18 months or later. PSH, permanent supportive housing; TAU, treatment as usual (Figure not reproduced here; see the original article.)

Overall, most studies (n = 10) demonstrated significant short‐ and/or long‐term benefits of PSH on housing stability (Aubry et al., 2016; Cherner et al., 2017; Lipton et al., 1988; Martinez & Burt, 2006; Sadowski et al., 2009; Stefancic & Tsemberis, 2007; Stergiopoulos et al., 2015; Stergiopoulos et al., 2019; Tsemberis et al., 2004; Young et al., 2009). One study showed that PSH had a benefit not only in improving the number of days spent in stable housing but also in similar improvements in residential stability over time, compared to treatment as usual (TAU). Of note, however, is that this study did have an unexpectedly large number of participants who were already in stable housing prior to enrolment in the study (Hwang et al., 2011). Of the 15 studies evaluating housing stability, one found no difference with supportive housing (Siegel et al., 2006) and another favoured staffed group homes over independent living, though only for minority groups (Goldfinger et al., 1999). An additional study found differing results, based on interaction with gender (Rich & Clark, 2005). In one study that examined hybrid models of housing, integrative services were found to have improved residential stability compared to parallel housing (McHugo et al., 2004).

Pooled data from the multicity Canadian At Home‐Chez Toi (n = 2148) and US Pathways (n = 225) trials found that an increased number of participants remained in stable housing within the PSH intervention group, compared to TAU, with an OR of 3.58; 95% CIs, 2.36, 5.43 (GRADE certainty of evidence: Moderate) (Aubry et al., 2016; Tsemberis et al., 2004). Both trials were RCTs, enlisting participants with serious mental illness, and were based on the “Pathways to Housing” Housing First (HF) Model, which involved providing participants with scattered‐site apartments alongside ACT or ICM (Aubry et al., 2016). The At Home‐Chez Toi initiative found that over the 2‐year follow up period, participants in the intervention arm spent 73% of the time in stable housing, compared to 32% in the TAU group (Aubry et al., 2016). The individuals who obtained stable housing also moved into housing more rapidly than the TAU participants (72.9 vs. 219.7 days, AAD = 146.4, CI, 118.0–174.9, p < .001). Long‐term analysis of a single site of the At Home‐Chez Toi study, in Toronto, Canada, found that the number of days spent stably housed remained significantly higher in participants in the HF groups than participants in the TAU groups, at all time points, with a median duration of follow up of 5.4 years (Stergiopoulos et al., 2019). The Pathways to Housing Project, based in New York City, similarly found that participants in the intervention group experienced faster reductions in their homelessness statuses and increased their housing stability relative to participants in TAU (F‐4137 = 10.1, p < .001; F 4137 = 27.7, p < .001) over a 2‐year follow‐up period, with an approximately 80% housing‐retention rate. Over 90% of participants in this study had coexistent SUDs (including alcohol) in conjunction with severe mental illness (Tsemberis et al., 2004).

Several other studies also showed improvements in housing status with supportive housing compared to TAU (Cherner et al., 2017; Lipton et al., 1988; Martinez & Burt, 2006; Sadowski et al., 2009; Stefancic & Tsemberis, 2007; Young et al., 2009). Among homeless individuals (n = 236) with a high prevalence of mental illness (86%) and SUDs (91%) in a study out of San Francisco, 81% of participants remained in supportive housing for at least 1 year, 63% for at least 2 years, and 48% for at least 3 years (Martinez & Burt, 2006). A Canadian study in Ottawa found improved rates of housing retention at 2 years in the HF Group (76% vs. 50.8%, p < .001) in participants with problematic substance use (n = 178), with the HF intervention group demonstrating higher housing stability and decreased time to move into housing, compared to the TAU group (MD −68.73 days, 95% CI, −125, −12.08, p < .05) (Cherner et al., 2017). However, another Canadian quasi‐experimental study from Toronto (n = 112) had mixed findings; participants in supportive housing had spent significantly more days in stable housing in the 6 months prior to the study, compared to the TAU group (F1,87 = 15.65, p < .01), but residential stability over time improved equally between the two groups. A large number of participants had already been in stable housing before their study enrolment and independent assignment into groups; only five participants remained homeless throughout the study period (Hwang et al., 2011).

In contrast, some studies either showed no difference between PSH or favoured more traditional or a continuum of interventions. Goldfinger et al., (1999) compared the provision of independent housing to staffed group‐home sites and reported a reduction in days spent homeless for staffed group homes over the independent living group, though only for minority groups (Goldfinger et al., 1999). Another quasi‐experimental study found no significant difference in the percentage of tenants in initial housing placement (n = 157) at 6, 12 and 18 months, between supportive housing versus community residences reliant on sobriety as a precondition for housing (Siegel et al., 2006). McHugo et al. studied two hybrid approaches to housing, “parallel housing” (resembling supportive housing + ACT) and “integrated housing” (resembling the traditional continuum model, whereby decisions regarding housing are influenced by clinicians), due to cited practical considerations, such as the shortage of safe low‐income housing. Within the parallel‐housing model, ACT teams helped participants to find affordable low‐income housing but did not have control over the housing supply itself. Similar to the PSH model, housing services were not dependent on participant's mental‐health treatment. Within the integrated housing model, a single agency provided both comprehensive mental health and controlled housing but did not necessarily require scattered‐site accommodation; congregate settings were felt to be appropriate for some patients. In this study, though both approaches reduced the incidence of participants obtaining functional housing and increased their time in stable housing, the integrated‐housing approach showed benefits over the parallel‐housing‐services group, in terms of the proportion of days of functional homelessness (group × time F value 0.56, d = −0.52, p < .05) and days in stable housing (group × time F value 1.38, d = 0.51) (p < .05) (McHugo et al., 2004).

Effect of gender

Interestingly, McHugo et al. found that the effect of the group on stable housing interacted with the effect of gender (F 1,107 = 8.32, p = .005,) with males in the parallel‐housing‐services group spending significantly less time in stable housing compared to other groups for whom the outcomes were all approximately equal, specifically for females in parallel housing and males and females in the integrated housing services (McHugo et al., 2004).

The gender effect was also explored by Rich and Clark (2005). In contrast to the above study by McHugo et al, this quasi‐experimental study found that homeless men within the comprehensive housing programme actually improved their time in stable housing (similar to PSH model), as compared to those in specialised case management. Men in the comprehensive housing programme increased their number of days in stable housing by 76 out of an average of 180 days, whereas males in specialised case management increased their housing by only 37 days (a difference of 39 days). Women significantly improved their homelessness in both programmes, but women in the specialised case management had more time stably housed than women in the comprehensive housing programme, likely due to women in comprehensive housing spending more time in psychiatric hospitals (Rich & Clark, 2005).

Adolescents

Two subgroup analyses of the At Home‐Chez Toi study were presented. One subgroup analysis, adjusting for study city and ethnoracial and Aboriginal status, found that homeless youth aged 18–24 in the intervention arm were stably housed for a mean of 65% of days, compared to 31% for the TAU youth (p < .001) (Aubry et al., 2016). The difference in the changes in the mean for housing stability for those aged 18–24 years compared to adults more than 24 years old was nonsignificant. Another analysis comparing older (50 years or older) and younger (18–49 years old) homeless adults demonstrated that HF had a similar effect of housing stability on those in the older and younger age groups at 24 months, compared to the TAU group (Aubry et al., 2016).

Substance Use

The evidence was mixed for the effects of substance use on housing retention. Some studies found there was no relationship between SUD and housing stability (Aubry et al., 2016; Martinez & Burt, 2006) whereas one study found it correlated with more days homeless (Goldfinger et al., 1999) (though this may be because of a relatively small number of participants, in the sample, without SUD). A subanalysis of the multicity Canadian At Home‐Chez Toi study found that people with SUD spent less time in stable housing in both the HF and TAU groups but that the HF initiative improved housing stability equally among participants with and without SUD (OR 1.17, 95% CI, −0.77, 1.76) (Aubry et al., 2016). A 5‐site (4 city) study in the United States found that, depending on the treatment site, the effect of intervention varied with substance abuse (Goldfinger et al., 1999).

Outcome 2: Mental health

Eleven studies examined the effects of PSH on mental health (Aubry et al., 2016; Cherner et al., 2017; Hwang et al., 2011; Lipton et al., 1988; McHugo et al., 2004; Rich & Clark, 2005; Sadowski et al., 2009; Siegel et al., 2006; Stergiopoulos et al., 2015; Tsemberis et al., 2004; Young et al., 2009). Only one study showed a benefit of PSH, over the TAU, on mental‐health outcomes (Rich & Clark, 2005) In three studies, psychiatric symptoms were somewhat improved in the comparison group, compared to supportive housing (Aubry et al., 2016; Cherner et al., 2017; Young et al., 2009). One study examined hybrid housing models and found improved psychiatric symptoms in integrated housing, compared to parallel housing (McHugo et al., 2004).

Most studies (n = 5) found no significant differences between PSH and TAU (Hwang et al., 2011; Lipton et al., 1988; Sadowski et al., 2009; Stergiopoulos et al., 2015; Tsemberis et al., 2004). Some studies (n = 2) found that mental‐health symptoms decreased over time for both groups, even though there was no group difference between intervention arms (Sadowski et al., 2009; Tsemberis et al., 2004), while two studies (of which one was a moderate‐needs population of the At Home‐Chez Toi study) did not find any significant differences, either with time or between groups (Hwang et al., 2011; Stergiopoulos et al., 2015). One study reported that participants in PSH experienced fewer psychiatric symptoms over time (p < .06) (Rich & Clark, 2005). However, significant differences between the groups, on these measures at baseline, suggest that their initial values may have accounted for these differences.

A few studies (n = 3) found some improved mental‐health symptoms in the comparison group, as opposed to supportive housing (Aubry et al., 2016; Cherner et al., 2017; Young et al., 2009). The multicity At Home‐Chez Toi trial found that though there were improvements in mental‐health symptoms and psychological integration in both groups (pooled SMD 0.70 and pooled SMD 0.53 respectively), the TAU had a small group benefit at final follow‐up (ASMD, 0.17; CI, 0.05–0.30; p = .01) (Aubry et al., 2016). Another 2‐year study of homeless adults with problematic substance use similarly found improved mental‐health symptoms in the TAU group at the end of the study (p < .01) (Cherner et al., 2017).

There may be a differential effect of the intervention, based on the type of mental‐health symptom. A 2‐year quasi‐experimental study using the 53‐item Brief Symptom Inventory, found that both interventions similarly improved symptoms in the following areas: psychoticism, depression, anxiety, obsessive‐compulsive disorder, interpersonal sensitivity and phobic anxiety (Young et al., 2009). However, greater improvements in somatisation, paranoid ideation and global mental‐health‐symptom severity was noted in the “Comprehensive, Continuous Integrated System of Care (CCISC)” model, (an intervention that is based out of a traditional substance‐abuse treatment agency), as compared to the ACT and supportive‐housing (ACT‐SH) intervention. Of note, however, is that compared to the ACT‐SH intervention, the residential CCISC programme had a higher intensity of mental‐health interventions, with on‐site services designed to address mental‐health symptoms in a population with severe coexisting mental‐health and SUDs (Young et al., 2009).

In one published study with no data reported, the effect on mental health was unclear (Siegel et al., 2006).

McHugo et al's study that compared two hybrid approaches to housing, “parallel housing” (resembling supportive housing + ACT) and “integrated housing” (resembling the traditional model) found that participants in the integrated‐housing model had less severe psychiatric symptoms during the 18 month follow‐up period as reported by the Colorado Symptom Index (CSI) (McHugo et al., 2004).

The At Home‐Chez Toi study also published an analysis of past‐month suicidal ideation over a 2‐year follow‐up period. In both groups suicidal ideation decreased from baseline (p < .001), though there was no differential effect of the intervention arm compared to TAU. There was also no significant difference between groups in the number of suicide attempts (HF 11.9%, TAU 10.5% (Aubry et al., 2016).

Gender

One study found that changes in psychiatric symptoms were not dependent on the participant's gender (Rich & Clark, 2005).

Adolescents

A subgroup analysis of the At Home‐Chez Toi study, comparing younger (18–49 years old) and older (>50 years old) homeless adults, found that older adults in the intervention arm experienced significantly more improvement from baseline to 24 months, compared to the TAU group, in both the mental‐component summary score of the SF‐12 (+3.82, 95% CI, 0.46–7.19) and the severity of mental‐health symptoms (−3.39, 95% CI, −6.24 to −0.54). (Chung et al.), as measured by the modified Colorado Symptom Index (Aubry et al., 2016). Another subgroup analysis of the same trial showed no significant group x time interaction in mental‐health symptoms, also using the SF‐12 Mental Health and Colorado Symptom Index tools, in the HF vs the TAU groups among youth aged 18–24 years (Aubry et al., 2016).

Outcome 3: Quality of life

The subjective quality of life was examined in eleven studies (Aubry et al., 2016; Cherner et al., 2017; Goldfinger et al., 1999; Hwang et al., 2011; McHugo et al., 2004; Rich & Clark, 2005; Sadowski et al., 2009; Siegel et al., 2006; Stergiopoulos et al., 2015; Stergiopoulos et al., 2019; Tsemberis et al., 2004). The data on the differential benefits of the HF versus the comparison groups was mixed. Some condition‐specific quality‐of‐life parameters may be improved with HF strategies. The housing approach may have a gender‐related effect, though this requires more research.

The At Home‐Chez Toi RCT found that the quality of life of both groups improved over time, with a moderate to large effect size (pooled SMD 0.76). HF participants improved more rapidly in the 1st year and had higher average scores over the study period (ASMD, 0.15; p < 0.01, CI, 0.04–0.24) but the difference narrowed over time and was no longer significant at the final interview (21 or 24 months) (ASMD at the final interview, 0.05; CI, 0.08–0.18, p = .43) (Aubry et al., 2016). Additional exploratory analyses showed that although there was no significant improvement over time in the generic quality of life via the EuroQOL 5 dimensions (EQ‐5D) visual analogue scale, within the HF intervention group there was a significant improvement in the condition‐specific quality of life from the baseline to 24 months, specifically the total condition‐specific quality‐of‐life measures and the subscales relating to leisure, living and safety, as reported from the Lehman Quality of Life Interview (QOLI‐20) index. The family domain of the condition‐specific quality of life had a significant 3‐way interaction with the treatment x the time x the site, due to the differing treatment effects by site at 24 months (Stergiopoulos et al., 2015). A single‐site extension of this study, with a median duration of follow‐up of 5.4 years, showed no difference in either the generic or disease‐specific quality of life between the HF and TAU groups. However, for this long‐term analysis, it is notable that within the disease‐specific QOL, only the global quality of life (“How do you feel about your life as a whole”) within Lehman's 20 item QOL interview was analysed (Stergiopoulos et al., 2019).

Two other studies reported improvements in quality of life in the intervention arm, compared to TAU (Hwang et al., 2011; Tsemberis et al., 2004). Hwang et al., 2011 assessed the quality of life over 18 months, with the EQ‐5D and the Lehman Brief Quality of Life Interview, of homeless individuals (n = 112) in Toronto, Canada, with severe and persistent mental illness. This study also found some improvements in the quality of life that were independent of the housing group, assessed via Lehman's Brief Quality of Life interview; these improvements were specifically in general life satisfaction (p = .02), satisfaction with finances (p < .01) and satisfaction with safety (p < .01). However, the HF intervention arm had additional significant benefits in terms of the score for satisfaction with the living situation, compared to the usual care (p < .01, time F, 3, 3, 261 = 47.68; group × time, F3,3,261 = 14.60, p < .01). Similar to other studies, there were no significant benefits between groups or with the time, as measured in the EQ‐5D quality‐of‐life assessment tool (Hwang et al., 2011). Another study also found benefits to the quality of life in the experimental arm, whereby participants who suffered from severe psychiatric illnesses had significantly improved life satisfaction in six of seven life domains within the Lehman Quality of Life scale (Tsemberis et al., 2004).

A study by Sadowski et al. (2009) noted improvements in quality of life over time compared to baseline in both groups, though it did not show any appreciable statistically significant differences between treatment arms. However, this trial used mental‐health and physical functioning subscales from the AIDS Clinical Trials Group 21‐Item Short Form instrument to determine and define “quality of life” (Sadowski et al., 2009). Schutt et al. (1997) also reported that quality of life, measured via life satisfaction, was unrelated to housing type (Goldfinger et al., 1999).

Two studies reported a benefit by comparison group over HF strategies (Cherner et al., 2017; McHugo et al., 2004). In assessing the effect of HF on homeless adults with problematic substance use, Cherner et al., 2017 found that the comparison group reported a higher quality of life at 24 months than the HF clients (d = −0.38; 95% CI, −0.74, −0.02; p < .025), though both groups had an improvement in their total score for quality of life from the baseline. McHugo et al. (2004) investigated the effect of two hybrid approaches to housing for adults with severe mental illness:“parallel housing” (resembling supportive housing + ACT) and “integrated housing” (resembling the traditional continuum model). Improvements over time for general life satisfaction were demonstrated over the study period for both populations, though the integrated‐housing‐intervention arm had a significant additional group benefit (F 6.35, p < .05) (McHugo et al., 2004).

The effect of housing intervention on quality of life was unclear in one study (no data reported) (Siegel et al., 2006).

Effect on gender

One study that examined hybrid approaches to housing investigated the interaction between gender and housing. At the end of the study, male and female participants in integrated housing services and female participants in supportive housing reported similar levels of life satisfaction whereas, in comparison, males in the parallel housing services had less satisfaction (McHugo et al., 2004).

The effect of gender on changes in perceived quality of life was unclear in one study (Rich & Clark, 2005).

Adolescents

In one subgroup analysis, older adults (>50 years) as compared to younger adults (18–49 years) in the HF intervention had significantly greater improvements in condition‐specific quality of life (+6.99, 95% CI, 1.39–12.59) versus the TAU over a 24‐month follow‐up period. Changes from the baseline compared to the TAU for generic quality was not statistically significant between older and younger homeless adults (Aubry et al., 2016). Another subgroup analysis of the same trial showed that in adults 24 years or younger, satisfaction with leisure (the leisure category of the QOLI‐20) at 24 months as well as total‐condition‐specific quality of life at 6 months significantly improved in the HF group compared to the TAU, though these differences were not significant in the overall treatment group × the time analysis (Aubry et al., 2016). Of note, however, is that the study size may have not been sufficient to detect differences between groups.

Outcome 4: Substance use

The effect of permanent housing on substance use was reported in nine trials (Aubry et al., 2016; Cherner et al., 2017; Hwang et al., 2011; McHugo et al., 2004; Rich & Clark, 2005; Stergiopoulos et al., 2015; Stergiopoulos et al., 2019; Tsemberis et al., 2004; Young et al., 2009). The results were mixed, though most studies found no difference in substance use with PSH.

Three studies reported improvements in alcohol and drug use in both groups, over time, but no differential benefit of the HF initiative (Aubry et al., 2016; Stergiopoulos et al., 2019; Young et al., 2009). The first, the multicity At Home‐Chez Toi RCT had a pooled decrease in the mean symptom count of 30% in both the HF and TAU groups, without an independent group benefit (Aubry et al., 2016). Similarly, a single‐site long‐term extension of the At Home‐Chez Toi study reported improvements in substance‐use severity in both groups over time, regardless of the intervention (Stergiopoulos et al., 2019). Another trial, a quasi‐experimental study with 163 participants with coexisting severe mental‐ and SUDs, also found reductions in substance use (rates of drug abstinence and average number of days of alcohol use in the past month) in both study groups, over time, with no significant difference between groups at 6 months (Young et al., 2009).

In addition to the lack of difference in substance use between groups, three other studies either did not report differences from the baseline or found no difference from the baseline over the study period (Hwang et al., 2011; Stergiopoulos et al., 2015; Tsemberis et al., 2004).

One study on homeless clients with problematic substance use found a benefit of the TAU group over the HF intervention, with regard to substantial or severe problems with drug use at 24 months. (OR = 0.34; 95% CI, 0.16–0.72; p < .01). The same study reported no group differences in problems associated with alcohol use, though both groups decreased their alcohol consumption over time (Cherner et al., 2017). In contrast, a single‐site study of the At Home‐Chez Toi trial within an ethnically diverse population in Toronto, Canada, noted that, at the end of 24 months, there was a 53% reduction in the days spent experiencing alcohol problems as well as a significant reduction in the amount of money spent on alcohol in the last 30 days (−$52.86, 95% CI, −104.29 to −1.43) in the HF‐ICM group compared to the TAU group. Secondary analysis showed a significant reduction in the number of days experiencing alcohol problems that was higher in the foreign‐born HF compared to Canadian‐born participants (ratio of rate ratios = 0.19, 95% 0.04‐0.88) (Stergiopoulos et al., 2015).

Hybrid approaches to housing (“integrative” versus “parallel” housing) were investigated in a single study. It found no statistically significant difference in the reported days of alcohol use or reported days of drug use both between groups as well as over time. Of note, analysis for this outcome had a lower statistical power as it was restricted to individuals who reported use at the baseline (McHugo et al., 2004).

Gender

The interaction between gender, type of interaction and days of alcohol use and days of illegal drug use was not significant in one study, though there was a trend for males in the specialised case‐management programme to have higher scores on those measures (Rich & Clark, 2005).

Adolescents

The severity of substance‐use problems was not statistically significant between older (>50 years) and younger (18–49 years) adults, for the HF compared with the TAU participants after 24 months, in one subgroup analysis (Aubry et al., 2016). Another publication depicting a subgroup analysis of the same study found no significant group × time interaction in substance use in the HF vs TAU groups in adolescents aged 18–24 years (Aubry et al., 2016).

Outcome 5: Hospitalisation

Ten studies examined hospitalisations data (Aubry et al., 2016; Goldfinger et al., 1999; Hwang et al., 2011; Lipton et al., 1988; Martinez & Burt, 2006; McHugo et al., 2004; Sadowski et al., 2009; Siegel et al., 2006; Stergiopoulos et al., 2015; Tsemberis et al., 2004) In multiple studies, HF strategies reduced the number of days in hospital and inpatient admissions.

The multicity At Home‐Chez Toi RCT found that both the HF and TAU groups had similar decreases in the number of days hospitalised and emergency department (ED) visits, with a pooled decrease of 62% and 53%, respectively. The HF group initially showed a significant reduction in ED visits at 6 months (p = .007), though this difference narrowed at the end of the study period (21 or 24 months, incident rate ratio = 0.80; CI, 0.65–1.00; p = .05). The rates of hospital admissions were not significantly different between the two groups, though the risk of 1 or more hospitalisations varied by site; for example, Site C showed 1.67 (95% CI, 1.08–2.59) (Aubry et al., 2016; Stergiopoulos et al., 2015).

Multiple other trials also found benefits of the HF intervention over the TAU (Lipton et al., 1988; Martinez & Burt, 2006; Sadowski et al., 2009; Tsemberis et al., 2004). A RCT from Chicago, Illinois (n = 405), found that after adjusting for the baseline characteristics and using zero‐inflated negative binomial models, there were statistically significant 29% reductions in hospital days and hospitalisations and a 24% reduction in ED visits in the HF group compared to the usual care (Sadowski et al., 2009). PSH also reduced the likelihood of being hospitalised (from 19% to 11%), the mean number of inpatient admissions per person (from 0.34 to 0.19 admissions per resident) and total number of inpatient admissions (45% decline, from 80 to 44) in a sample of 236 adults (most of whom had a dual diagnosis of mental illness and SUD), in San Francisco, California (Martinez & Burt, 2006). In this trial, emergency‐room visits from year 1 to 2 were also reduced in the intervention group compared to the control group (regression coefficient B = −7.07, SE = 1.29; p < .01 (Martinez & Burt, 2006). In another US‐based trial, a Pathways to Housing RCT, the control group spent more time in hospital compared to the HF group (F1195 = 74, p < .01) over the 2‐year follow‐up period. (Tsemberis et al., 2004). There were also statistically significant differences in the number of days hospitalised in a study by Lipton et al. (1988), where the experimental group spent a mean of 55 nights or 15% of the study year in a hospital compared to the control who spent a mean of 168 nights or 46% of the year in hospital (t = 3.74, df = 20, p < .001), with no differences in the number or length of readmissions to psychiatric hospitals (Lipton et al., 1988).

Two studies found no statistically significant differences in health‐care utilisation (including both inpatient and outpatient care) between supportive housing and usual care over time (Hwang et al., 2011; Goldfinger et al., 1999). One study (Hwang et al., 2011) reported health‐care utilisation by participants who self‐report, whereas the second reported service use via case management records from community mental‐health centres and affiliated clinics, and the Massachusetts Department of Mental Health and Medicaid for inpatient admissions (Goldfinger et al., 1999).

Adolescents

A sub‐group analysis of the At Home‐Chez Toi study found no significant group x time interaction in adolescents aged 18–24 years between the HF and TAU groups, for the number of ED visits or percentage of persons who visited a clinical provider (Aubry et al., 2016).

Outcome 6: Employment

One study, the At Home‐Chez Toi study reported the effect of PSH on employment outcomes (Aubry et al., 2016). Here, 2148 people who were homeless and were diagnosed with a mental illness were recruited from five Canadian sites. They were subsequently grouped into “moderate” or “high needs” groups, where participants with high needs received ACT and those with moderate needs received ICM, with a median follow‐up after 745 days. Compared with the control group of moderate‐needs participants, the HF ICM participants had lower odds of obtaining employment. Over time, the odds of obtaining employment in both the HF‐ICM and ACT groups improved compared to the control, but despite this, the rates of employment in the HF group never exceeded those of the control group. For the ACT high‐needs group, the odds of obtaining employment was not statistically significant compared to the control group. Men, younger participants and those employed at the baseline had increased odds of obtaining competitive employment in both the HF‐ICM and HF‐ACT groups compared to the control. In the HF‐ICM group, individuals with more than 12 years of education and a higher MCAS (Multinomah Community Ability score) also had a higher chance of obtaining competitive employment. Secondary employment outcomes, such as job tenure in days, hours worked per week and hourly wage, were not statistically significant between the HF and control groups. Interestingly, the low rates of employment in the study were in contrast to the high percentage (74%) of individuals who stated a desire to return to employment (Aubry et al., 2016).

Outcome 7: Income

The At‐Home‐Chez Toi study also examined the effect of HF on income. There were no statistically significant differences between Housing First and control‐group income from various sources over time (Aubry et al., 2016). These results were consistent with a study by Rich and Clark (2005), where the three‐way interaction between time, gender and type of intervention for income in average dollars/month was also not statistically significant at the 12‐month follow up (Rich & Clark, 2005).

Income‐assistance intervention

Outcome 1: Housing stability

Ten eligible studies assessed the effectiveness of income‐assistance interventions on housing stability. Five studies assessed the effectiveness of income assistance in the form of rental subsidies (Gubits et al., 2018; Hurlburt et al., 1996; Pankratz et al., 2017; Rosenheck et al., 2003; Wolitski, 2009). For people with acquired immunodeficiency syndrome (AIDS), Wolitski et al. (2009) examined a federal programme that provided immediate housing opportunities in the form of rental assistance along with case management. They found that this programme was associated with a higher percentage of participants housed in their own place up to 18 months into the programme, compared with customary housing services and case management (at 6 months: OR = 6.20; 95% CI, 4.18–9.20; p < .0001; at 18 months: OR = 4.60; 95% CI, 3.10–6.83; p < .0001) (Wolitski 2009). Participants receiving priority access to housing vouchers along with case management demonstrated more days stably housed in the past 90 days (over 3 years: MD = 8.58; p < .004; GRADE Certainty of Evidence: Low) (Rosenheck et al., 2003) and were significantly more likely to achieve stable independent living arrangements than the controls who only received case management (over 24 months: 57.5% vs. 30.4%; OR = 3.09; 95% CI, 2.00–4.76; p < .0001) (Hurlburt et al., 1996).

Five studies investigated the effect of income‐assistance interventions delivered in alternative formats and which included financial‐empowerment education, compensated‐work therapy, and IPS (Booshehri, 2017; Ferguson, 2018; Forchuk et al., 2008; Kashner, 2002; Poremski et al., 2015). A 28‐week financial‐empowerment education programme was compared with employment training for low‐income families with children. No significant differences in the housing conditions were identified between the study and the control groups after the intervention was undertaken (Ferguson, 2018). A compensated work‐therapy programme (CWT) that combined supported employment with stepwise clinician‐run therapy offered to homeless veterans with substance dependency was compared with standard access to comprehensive rehabilitation, addiction, and psychiatric and medical services (Kashner, 2002). A significantly reduced odds of an episode of homelessness was detected in the study group participants who were offered supported employment, compared with the controls (OR = 0.1; 95% CI, 0.1–0.3; p = .001; GRADE certainty in evidence is low). However, no significant improvement on housing stability was observed among the study group of homeless youth experiencing mental illness who received extra IPS, through regular meetings with employment specialists, on top of the 20‐month social‐enterprise intervention programme that included the same vocational skills classes and case management services that were also offered to the controls (Ferguson, 2018). The diverse study designs and participant profiles, along with smaller sample sizes, might contribute to the inconsistency and inconclusive effects measures. Forchuk et al. (2008) examined the effect of adding fast‐tracked income support on top of housing assistance for individuals who were discharged from psychiatric wards to shelters and who were precariously housed. A significant improvement in the percentage of participants attaining independent housing at 6 months was detected in the study group when compared with the controls who only received the usual care with housing support by referral (100% vs. 14.2%; OR = 65; 2.23,1887.35; p < .001). Income assistance in the form of rental subsidies was consistently associated with better housing stability among the eligible studies.

Outcome 2: Mental health

Six studies assessed the impact of income‐assistance intervention on mental health (Booshehri, 2017; Ferguson, 2018; Gubits et al., 2018; Kashner, 2002; Rosenheck et al., 2003; Wolitski, 2009). The effect of income‐assistance interventions on mental health varied depending on the intervention characteristics. Immediate rental assistance with case management for people with AIDS led to improved depression symptoms and perceived stress level at 6 months but it did not show a consistent effect on self‐reported mental‐health statuses compared to the usual care (Wolitski, 2009). Permanent housing subsidies for homeless families with children aged 15 years or younger was associated with decreased psychological distress compared with the usual access to community housing services (Gubits et al., 2018). However, housing vouchers combined with case management for homeless veterans with psychiatric or addiction/alcohol disorders did not generate significant improvements in the mental‐health statuses of the participants (Rosenheck et al., 2003). One study that assessed IPS programmes for homeless youth reported higher self‐esteem scores (23.00(SD = 4.88) vs. 21.50(SD = 5.91), p < .05), less self‐reported depression symptoms (4.85 vs. 6.71, p < .10), and less self‐reported attention‐deficit hyperactivity (ADHD) (5.54 vs. 7.06, p < .01) symptoms (Ferguson, 2018). Nevertheless, financial‐empowerment education programmes for low‐income families, compared to existing employment training, did not provide additional benefits on the ability to manage stress or the presence of depression symptoms (Booshehri, 2017). The CWT programme offered to homeless veterans with substance dependence, in one study, was not associated with significantly different mental‐health status when compared with access to standard rehabilitation, and addiction and mental‐health services (Kashner, 2002).

Outcome 3: Quality of life

Three studies examined the effect of income‐assistance intervention on quality of life (Ferguson, 2018; Pankratz et al., 2017; Rosenheck et al., 2003). One study showed that additional rent assistance with a top‐up of 350 Canadian dollars led to significant improvements in quality of life at 6 months compared to the usual housing support (Pankratz et al., 2017). For veterans with a diagnosis of a major psychiatric disorder or an alcohol/drug disorder who were homeless or who had been homeless for 1 month or longer, priority access to housing vouchers did not provide additional benefits compared with the usual case management (Rosenheck et al., 2003). A social‐enterprise intervention that provided vocational and business skills classes was not associated with an increased satisfaction of life quality compared to SCM and support (Ferguson, 2018).

Outcome 4: Substance use

our studies examined the effects of income‐assistance intervention on substance use (Gubits et al., 2018; Kashner, 2002; Poremski et al., 2015; Rosenheck et al., 2003). For homeless veterans with substance dependence, CWT immediately reduced the consumption of alcohol and drugs within the first 3 months (β = −44.7%; 95% CI, −69.7% to −19.7%; t = 3.51; p = .001) (Kashner, 2002). The addition of priority access to housing vouchers for veterans with a diagnosis of a major psychiatric disorder or an alcohol/drug disorder, compared to existing case management, led to decreased days of drinking to intoxication (1.46 vs. 1.95, t = 0.73, p = .0053) and fewer days of alcohol use over the 3‐year study period (Rosenheck et al., 2003). However, no significant association was identified between priority access to housing subsidies and differences in the scores of the Addiction Severity Index (ASI) (Rosenheck et al., 2003). For homeless families with children aged 15 or younger, rental subsidies without case management did not lead to decreased use of substance compared to the usual community housing services (Gubits et al., 2018).

Outcome 5: Hospitalisation

Three trials evaluated the impact of income‐assistance intervention on hospitalisations (Kashner, 2002; Poremski et al., 2015; Wolitski, 2009). CWT for homeless veterans with substance dependence significantly decreased the number of mean inpatient days in medicine in 1 year (2.6 days vs. 0.3 days, t = 3.02, p = .003) but led to no significant difference in mean patient days in psychiatry or addiction wards (Kashner, 2002). The IPS programme, which aids in obtaining and maintaining competitive employment for individuals experiencing mental illness who are precariously housed or have been homeless for at least seven nights in Canada, did not show a decrease in the number of days spent in a hospital or correctional facility at a 3‐month interval (Poremski et al., 2015). Rental assistance combined with case management for people with AIDS was not associated with a decreasing trend in emergency room visits along an 18‐month study interval (Wolitski, 2009).

Outcome 6: Employment

Five studies assessed the effectiveness of income‐assistance interventions on employment outcomes (Booshehri, 2017; Ferguson, 2018; Gubits et al., 2018; Poremski et al., 2015; Rosenheck et al., 2003). Both long‐term housing subsidies for homeless families with children (Gubits et al., 2018) and housing subsidies with case management for homeless veterans with psychiatric or alcohol/drug disorders (Rosenheck et al., 2003) were unable to demonstrate a positive impact on employment. Likewise, the financial empowerment programme was not associated with an increase in employment status, whereas the standard job training and search programme offered to the controls demonstrated an increase in employment status (Booshehri, 2017). Furthermore, the reported effects of the IPS programme on employment outcomes also appeared inconsistent. Compared with SCM and service for homeless individuals with mental illness, the IPS programme contributed to significant improvements in obtaining employment during the 8‐month period of high‐intervention fidelity (OR = 2.418; 95% CI, 1.133–5.157; p = .02) (Poremski et al., 2015). On the other hand, the IPS programme with case management offered to homeless youth did not lead to improvements in employment when compared with the social‐enterprise intervention that included vocational‐ and business‐skills acquisition (Ferguson, 2018).

Outcome 7: Income

Six studies reported on the effectiveness of income‐assistance interventions on income outcomes (Booshehri, 2017;Ferguson, 2018; Gubits et al., 2018; Pankratz et al., 2017; Poremski et al., 2015; Rosenheck et al., 2003). For homeless families with a child aged 15 years old or younger, long‐term rent subsidies were associated with an increased percentage of households acquiring food security (61.1% vs. 51.5%, SE = 3.5, p < .01 at 37 months) (Gubits et al., 2018). However, self‐reported family earned income did not show a difference between the study and the control group. Homeless veterans with psychiatric or alcohol/drug disorders who received housing subsidies in addition to case management were not associated with increases in total income per month compared with the controls who only received case management (656 vs. 684, t = 1.56; p = 0.12) (Rosenheck et al., 2003). An 8‐month IPS to provide specialised assistance on employment for homeless individuals with mental illness did not result in a difference in wages per hour compared with the SCM (Poremski et al., 2015). Another IPS for homeless youth was compared with a social enterprise intervention that focused on vocational‐ and business‐skills acquisition over a 20‐month study period and was not associated with an increase in weekly income (Ferguson, 2018). In addition, a 28‐week financial‐empowerment education programme offered for low‐income families with a child and housing insecurity did not give rise to an increase in hourly earnings or relief of economic hardship when compared with standard weekly job training and search activities (Booshehri, 2017). Overall, the income‐assistance interventions were not associated with noticeable changes in income outcomes among participants in the eligible studies.

SCM and peer support interventions

Standard case management

Outcome 1: Housing stability

Nine trials reported on the effectiveness of SCM treatment on housing stability outcomes (Conrad et al., 1998; Graham‐Jones et al., 2004; Hurlburt et al., 1996; Lapham et al., 1996; Nyamathi et al., 2016; Sosin et al., 1995; Towe et al., 2019; Upshur et al., 2015; Weinreb et al., 2016). The positive effect of SCM on housing stability in homeless (addicted) male veterans (n = 358) showed significantly fewer homeless nights at 12 months in the intervention group (n = 187), an effect that was reversed at 24 months (certainty of evidence—low) (Conrad et al., 1998). An SCM trial with enhanced or intensive housing‐placement assistance (EPHA) for homeless single adults living in HIV emergency shelters (n = 236) reported significantly higher percentages of participants' placements in stable housing (p = .02; 25% placed by 150 days vs. 243 days) (Towe et al., 2019). A three‐armed quasi controlled trial with homeless patients registered temporarily either in a health centre advocacy group or an outreach advocacy group and the TAU found no significant differences observed between groups, although a higher number of participants in one group achieved housing outcomes (Graham‐Jones et al., 2004). A four‐arm trial (n = 361) assessing different CM intensities in persons who are homeless or at risk of homelessness and with severe or persistent mental illness reported no significant improvement observed in their housing outcomes (Hurlburt et al., 1996). A similar study reported no significant between‐group improvement in stable housing in groups of homeless alcohol abusers, however, significantly more favourable housing‐stability outcomes were observed among programme graduates than among dropouts (Lapham et al., 1996). Nyamathi et al. (2016) found no significant between‐group differences in either the peer‐coach‐non‐comprehensive case management group (NCM) or the usual care group after 12‐months in a population of homeless men recently released from California jails and prisons. Another study on homeless women with alcohol‐use problems found no significant difference between groups on housing outcomes between Project RENEWAL intervention and TAU. While those in the intervention group spent double the time in their apartments in 6 months, women in the TAU group spent significantly fewer nights in shelters (Upshur et al., 2015). A short‐term inpatient case‐management‐only intervention study reported a significant increase in the average number of days in residential stability (Sosin et al., 1995). Finally, a 6‐month clustered evaluating integrated care model for homeless mothers (ICMHM) versus TAU reported modest but no significant housing improvements, with more than half of participants still living in a shelter (Weinreb et al., 2016).

Outcome 2: Mental health

Four trials reported on the effectiveness of SCM on mental‐health outcomes (Conrad et al., 1998; Nyamathi et al., 2001; Upshur et al., 2015; Weinreb et al., 2016). A three‐arm trial (n = 948) with a nurse‐led case management (NCM) programme, peer‐mentored programme and standard/usual care for women in emergency or sober‐living shelters reported higher levels of hostility (p < .001) and depression symptoms (p < .05) compared to those female participants receiving standard care in the NCM after 6 months (Nyamathi et al., 2001). However, no significant difference in psychological well‐being was reported between groups using the Mental Health Index (MHI‐5). Another trial in homeless addicted male veterans with 3–6 months of stays at hospital facilities (residential care) plus case management versus TAU for 21 days reported no significant differences between groups on ASI's psychiatric‐symptoms sub‐score (Conrad et al., 1998). Another 6‐month trial of guideline‐based primary care provider brief intervention and referral to the CM for ongoing follow‐up visits (n = 42) for homeless women with alcohol use problems found reduced odds of depression at 3 months (OR, 0.38; 95% CI, 0.14–0.99) (Weinreb et al., 2016). The women did not show improvements in their overall mental‐health statuses, with no significant between‐group differences (MD, 4.50; 95% CI, −0.98–9.98), and a significantly lower percentage of participants met depression criteria at follow‐up, (Upshur et al., 2015).

Outcome 3: Quality of life

Two RCTs reported the effects of different SCM treatment on groups' quality of life outcomes (Graham‐Jones et al., 2004; Nyamathi et al., 2001). A three‐armed quasi controlled trial with homeless patients registered temporarily either in a health centre or under the care of outreach advocacy groups and TAU reported better improvements than the control group on the social‐isolation dimension only Graham‐Jones et al. (2004). In contrast, in a Nottingham health profile, the outreach group achieved better improvements in participants' emotional distress and sleep subscores (Graham‐Jones et al., 2004). Both intervention groups showed improvements on different subscales in the life‐fulfilment scale, while only the outreach advocacy group improved significantly on the aggregated fulfilments scales (Graham‐Jones et al., 2004). There were no significant between‐group differences in the Delighted‐Terrible Faces scale (Graham‐Jones et al., 2004). Also, a nurse‐led case‐managed programme compared with peer‐intervention for homeless women and their intimate partners with standard care programme reported no significant differences in the quality‐of life‐outcomes (Nyamathi et al., 2001).

Outcome 4: Substance use

Six studies reported on substance‐use outcomes with different SCM treatments (Conrad et al., 1998; Lapham et al., 1996; Nyamathi et al., 2001; Nyamathi et al., 2016; Sosin et al., 1995; Upshur et al., 2015). Homeless male veterans with addictions problems with three to 6 months of hospital stays plus case management showed better improvements in the alcohol‐ and drug‐use composite scores, but these were short‐lived compared to TAU after 24 months (Conrad et al., 1998). A three‐arm trial reported reductions in average days of alcohol and drug consumption in a case‐management‐only group, a CM‐with‐supported‐housing group in graduates of short‐term in‐patient substance‐use programme who lacked housing (Sosin et al., 1995). Homeless alcohol abusers who were offered different intensities of SCM (n = 469) showed no significant between‐group differences in days of alcohol use (Lapham et al., 1996). Similarly, a three‐arm trial with homeless women and their intimate partners found no significant differences in substance‐use outcomes between groups: a peer‐mentored group, a group in a nurse case‐managed programme, and one in an SCM programme (Nyamathi et al., 2001). Another 12‐months trial on homeless men recently released from jails/prisons who were exposed to weekly peer coaching, intermediate peer coaching compared with the usual treatment did not find any significant effects on substance‐use outcomes (Nyamathi et al., 2016). An RCT with homeless women with alcohol‐use problems who received brief guideline‐based interventions from primary care providers and referrals to the CM for ongoing follow‐up visits for 6 months did not find any significant between‐group differences on alcohol‐consumption rates, percentages of completely abstained participants, or negative consequences of alcohol use, respectively (Upshur et al., 2015).

Outcome 5: Hospitalisation

One trial evaluated the impact of a health advocate‐SCM (with or without outreach registration) on hospitalisations over 3 months (Graham‐Jones et al., 2004). Only five percent of all participants in the study accessed the emergency department, with no significant difference between health advocacy or usual‐care groups (Graham‐Jones et al., 2004).

Outcome 6: Employment

Four trials reported on the effects of different SCM interventions on the employment of participants (Conrad et al., 1998; Lapham et al., 1996; Nyamathi et al., 2016; Weinreb et al., 2016). The impact of SCM interventions on the employment outcomes of homeless (addicted) male veterans (residents‐to‐case managers ratio of 10:1 and 25:1 for the residency and community follow‐up phases) reported significant improvements favouring the intervention group over the entire study period (Conrad et al., 1998). In another four‐arm trial on homeless alcohol abusers (n = 469) there were no significant between‐group differences in improvements in employment (Lapham et al., 1996). Also, a three‐arm trial (n = 600) with a nurse case‐managed programme, and peer‐mentored intervention compared to TAU in homeless women and their intimate partners reported some improvements in employment but no statistically significant differences between groups after 6 months. A 6‐month clustered trial of an integrated‐care model for homeless mothers (ICMHM) with major depressive disorder showed that participants' employment improved but there were still no significant between‐group differences (Weinreb et al., 2016).

Outcome 7: Income

None of the included RCTs reported on the effects of SCM on income.

Peer support interventions

Six randomised trials examined the effect of peer support interventions among individuals with lived experience of homelessness (Corrigan et al., 2017; Ellison et al., 2020; Lapham et al., 1996; Nyamathi et al., 2001; Nyamathi et al., 2016; Yoon et al., 2017). All six trials took place in the United States and among diverse and heterogeneous cohorts of patients, preventing us from pooling effect estimates using a random effects model.

Outcome 1: Housing stability

Of the six trials on peer‐support interventions among individuals with lived experience of homelessness, four examined housing stability (Corrigan et al., 2017; Ellison et al., 2020; Lapham et al., 1996; Nyamathi et al., 2016). Overall, none of the trials reported any added benefit associated with receiving peer‐support interventions compared to usual care; one randomised controlled trial (Corrigan et al., 2017) examined an ethnically matched peer‐navigator programme, compared to usual care among homeless African Americans with serious mental illness, and found that even though participants in both the intervention and usual‐care groups showed decreased homelessness rates over 12 months, the between‐group difference was not significant at 12 months (Intervention: 91%, control 84%, OR = 1.84; 95% CI, 0.40–8.43; p = .42). Another randomised controlled trial (Ellison et al., 2020) examined peer‐specialist intervention compared to usual care among homeless veterans receiving housing vouchers and measured the number of days participants spent housed in the past month, when using housing vouchers, as well as the number of days spent housed in any community accommodation in the past month. Investigators found no significant differences between the intervention and usual care groups across 12 months (p > .05). Comparably, one randomised controlled trial (Lapham et al., 1996) examined peer‐manager‐delivered support services alongside temporary housing, compared to temporary housing alone, among homeless individuals with problematic alcohol use, and measured the number of days in stable housing in the past month and over 10 months, using the Personal History Form (PHF). Investigators found that assignment to interventions with a peer‐support component was not significantly associated with increased housing stability compared to assignment to temporary housing alone (the coefficient estimate for assignment to peer support with temporary housing = 11.0 (SE 1.7); the coefficient estimate for assignment to temporary housing only = 13.3 (SE 2.0); the overall model coefficient of determination R2 = 0.09; p > .001). Finally, one randomised controlled trial (Nyamathi et al., 2016) examined a peer‐coaching programme compared to usual care among homeless men with a history of substance use who had recently been released from county jails. This study used a structured questionnaire to measure the percentage of participants who lived on the street or in shelters over 12 months. It found no added benefit of being assigned to the peer‐support programme compared to the usual care (intervention n = 20 (11.4%), the control (N = 19 (10.1%); OR = 1.14; 95% CI, 0.59–2.23; p = .68).

Outcomes 2: Mental health

Three trials examined mental‐health outcomes (Corrigan et al., 2017; Ellison et al., 2020; Nyamathi et al., 2001) and provided mixed evidence on the effect of peer‐support interventions on participants' mental health. One randomised controlled trial (Corrigan et al., 2017) examined an ethnically matched peer‐navigator programme compared to the usual care among homeless African Americans with serious mental illness and measured psychological distress using the Texas Christian University Health Forms (TCU‐HF). Investigators found that those in the intervention group reported better improvements across 12 months (4 months: intervention M = 23.0 (SD 8.04), control M = 5.2 (SD 8.92); 12 months: intervention M = 18.5 (SD 4.79), control M = 24.4 (SD 7.93); overall group by time effect p < .05). As well, investigators measured emotional well‐being, using the Short‐Form 36 (SF‐36) and similarly found better improvements in the peer‐support group compared to usual care across 12 months (4 months: intervention M = 63.0 (SD 16.6), control M = 71.1 (SD 16.1), overall group by time effect p < .05).

Conversely, one randomised controlled trial (Ellison et al., 2020) examined a peer‐specialist intervention compared to usual care among homeless veterans receiving housing vouchers and measured symptoms of mental illness using the 24‐item Behaviour And Symptom Identification Scale (BASIS‐24) up to 12 months and found no statistically significant between‐group difference (p > .05). Another randomised controlled trial (Nyamathi et al., 2001) examined an ethnically matched female peer‐mentorship programme compared to usual care among homeless women and their intimate partners, measuring psychological well‐being over 6 months using the Mental Health Index (MHI‐5) and found no statistically significant improvement among those receiving peer support compared to the usual care (Regression coefficient B = −5.17 (SE 2.2); p = .019). Moreover, the investigators used the Brief Symptom Inventory (BSI) to examine symptoms of depression, anxiety, and hostility over 6 months and reported that women and their partners who had received the peer‐support intervention were more likely to suffer from higher levels of depression (regression coefficient B=0.68 (SE, 0.3); p = .01), and anxiety (regression coefficient B = 0.76 (SE 0.3); p = .008), but not hostility (regression coefficient B = 0.44 (SE 0.3); p = .11) compared to those who received usual care. Finally, investigators measured self‐esteem over 6 months, using the revised version of the Self‐Esteem Inventory (SEI), and found no significant improvement associated with receiving peer support compared to the usual care (regression coefficient B = −1.08 (SE 0.5); p = .02).

Outcome 3: Quality of life

Evidence on the effect of peer‐support interventions on quality of life is scarce and mixed as only two trials examined this outcome (Corrigan et al., 2017; Nyamathi et al., 2001).

One randomised controlled trial (Corrigan et al., 2017) examined an ethnically matched peer‐navigator programme, compared to usual care among homeless African Americans with serious mental illness, measured participants' generic quality of life using the Lehman's quality of life interview, and found a significant between‐group difference favouring the peer‐support arm compared to the usual care across 12 months (effect size 0.1, 0.3; range of internal consistency 0.71, 0.82, no further details). However, in another randomised controlled trial (Nyamathi et al., 2001) on an ethnically matched female peer‐mentorship programme compared to the usual care among homeless women and their intimate partners examined life satisfaction over 6 months, using a series of faces with expressions ranging from very happy to very sad, and found no significant improvement associated with receiving peer support compared to the usual care (regression coefficient B = −0.27 (SE 0.2); p = .072).

Outcome 4: Substance use

Four trials examined substance‐use outcomes (Ellison et al., 2020; Lapham et al., 1996; Nyamathi et al., 2001; Nyamathi et al., 2016) and provided mixed evidence that suggests the attenuated effect of receiving peer support on substance‐use outcomes compared to the usual care. Only one randomised controlled trial found an added benefit associated with peer support (Lapham et al., 1996). Investigators examined support services delivered by peer managers alongside temporary housing compared to temporary housing alone among homeless individuals with problematic alcohol use and measured the number of days of alcohol use in the past month and over 10 months using the Addiction Severity Index. Their assessment found that assignment to interventions that came with a peer‐support component was statistically associated with decreased days of alcohol use compared to assignment to temporary housing alone (the coefficient estimate for assignment to peer support with temporary housing = 7.4 (SE 1.1); the coefficient estimate for assignment to temporary housing only = 7.1 (SE 1.3); the overall model coefficient of determination R2 = 0.14; p > .001).

One randomised controlled trial (Ellison et al., 2020) examined a peer‐specialist intervention compared to the usual care among homeless veterans receiving housing vouchers. It used the Addiction Severity Index to measure alcohol and drug use up until 12 months and found no statistically significant between‐group difference (p > .05). As well, another randomised controlled trial (Nyamathi et al., 2001) examined an ethnically matched female peer‐mentorship programme, compared to usual care among homeless women and their intimate partners, and measured the use of noninjection drugs over 6 months with a minimally revised Drug History Form and found no significant decrease in drug use associated with receiving peer support compared to the usual care (regression coefficient B = −0.30 (SE 0.3); p = .335). Finally, a third randomised controlled trial (Nyamathi et al., 2016) examined a peer‐coaching programme compared to usual care among homeless men who had recently been released from county jails and had a history of substance use. This trial measured the percentage of participants who were using different substance drugs over 12 months, using the modified version of the Texas Christian University (TCU) Drug History form, and found no statistically significant between‐group difference for marijuana use (intervention N = 85 (48.0%), control N = 85 (45.7%); OR = 1.09; 95% CI, 0.72–1.65; p = .65), heroin (intervention N = 22 (12.4%), control N = 24 (12.9%); OR = 0.95; 95% CI, 0.5–1.77; p = .89), or stimulant substances (intervention N = 80 (45.2%), control N = 95 (51.1%); OR = 0.79; 95% CI, 0.52–1.19; p = .26).

Outcome 5: Hospitalisation

Evidence on hospitalisation was limited. Only one randomised controlled trial (Yoon et al., 2017) examining a peer‐mentorship programme compared to usual care among homeless veterans measured inpatient admissions using the VA Medical Statistical Analysis System records and found no statistically significant difference between participants who received peer support and those who received usual care (intervention M = 0.2 (SD 0.7), control M = 0.2 (SD 0.7); t test = 0.3; p = .79). As well, investigators measured the number of emergency‐department visits and found a similar nonsignificant difference (intervention M = 1.4 (SD 3.0), control M = 1.3 (SD 2.3); t test = −0.5; p = .61).

Outcome 6: Employment

Two trials examined employment outcomes (Lapham et al., 1996; Nyamathi et al., 2016) and provided mixed evidence on the effect of peer‐support interventions on employment. One randomised controlled trial (Lapham et al., 1996) examining support services delivered by peer managers, alongside temporary housing, compared to temporary housing alone among homeless individuals with problematic alcohol use, used the Personal History Form to measure the number of days of employment in the past month and over 10 months, and found that assignment to interventions with a peer‐support component is statistically associated with increased days of employment (the coefficient estimate for assignment to peer support with temporary housing = 7.8 (SE 1.1); the coefficient estimate for assignment to temporary housing only = 7.0 (SE 1.3); the overall model coefficient of determination R2 = 0.22; p < .001).

Conversely, one randomised controlled trial (Nyamathi et al., 2016) examining a peer‐coaching programme, compared to usual care among homeless men recently released from county jails with a history of substance use, used structured questionnaires to measure the percentage of participants with full‐time and part‐time employment as well as the percentage of participants who were unemployed over 12 months. It found that the peer‐support intervention did not significantly increase the percentage of participants who had full‐time employment (intervention N = 21 (12.0%), control N = 35 (18.6%); OR = 0.59; 95% CI, 0.33–1.07; p = .08), or part‐time employment (intervention N = 24 (13.7%), control N = 28 (14.9%); OR =0.90; 95% CI, 0.50–1.63; p = .74), nor did it decrease the percentage of participants who reported being unemployed (intervention N = 130 (74.3%), control N = 125 (66.5%); OR = 1.45; 95% CI, 0.92–2.29; p = .1).

Outcome 7: Income

No trials examined the effect of peer‐support interventions on income‐related outcomes.

Mental health interventions

Assertive community treatment

Outcome 1: Housing stability

Five trials reported on the impact of ACT on housing stability (Clarke et al., 2000, Fletcher et al., 2008, Lehman et al., 1997, Morse et al., 1992, 1997, 2006). The effect of an ACT programme on homeless persons with mental illness found no significant between‐group difference regarding the number of days homeless in shelters; however, the ACT group spent more days in community housing compared to the TAU control group (Lehman et al., 1997). A 12‐month three‐arm trial for homeless people with severe psychiatric disorders treated with integrated‐ACT, drop‐in centre care and traditional outpatient treatment, found better improvements in housing stability in participants treated with continuous ACT than those in outpatient clinics or drop‐in centres, respectively (Morse et al., 1992). Also, a follow‐up trial on homeless persons with mental illness found better improvements in housing stability using individualised ACT, ACT with community workers and brokered case management (BCM), respectively (Morse et al., 1997). Another 24‐month trial using different ACT modalities (ACT only—ACTO, integrated ACT—IACT, nonintegrated ACT—NIACT) in homeless clients with severe mental illness and SUD reported p more days in stable housing at 18 months (p = .0021) and 24 months (p = .03), respectively than in the control group (Morse et al., 2006). However, there was no significant difference between ACT modalities. Also, a three‐arm ACT trial on homeless clients with severe mental illness and SUD reported that participants in both IACT and ACTO modalities had more days in stable housing than those in the SC group, but there were no significant between‐group differences between the ACTO and IACT modalities (Fletcher et al., 2008).

Outcome 2: Mental health

Seven RCTs and a follow‐up study reported on mental‐health outcomes in different ACT interventions (Essock et al., 1998, 2006; Fletcher et al., 2008; Lehman et al., 1997; Morse et al., 1992, 1997, 2006). A three‐arm trial with IACT with a substance‐use specialist, ACTO and standard care reported reductions in the mean scores of psychiatric symptoms at 3, 15 and 30 months using BPRS scale. While psychiatric symptoms were reduced in the ACTO/ACTI versus the SC comparisons, it was not statistically significant (p > .1) (Fletcher et al., 2008). In another 24‐month trial, participants receiving any of the interventions reported improvements over time in mental health at 6 months—2.01 (SD0.44), 1.94 (SD0.42), and 1.98 (SD0.58) as well as at 24 months—1.88(SD0.54), 1.66 (SD0.46) and 1.86 (SD0.60) for ACTO, IACT and the control groups, respectively (Morse et al., 2006). A follow‐up trial found no between‐group differences in the group modalities and the treatment condition had no effect on psychiatric symptoms (p = .19) (Morse et al., 2008). A post hoc analysis of a previous three‐arm treatment of homeless mentally ill individuals with ACT, ACT with community workers and BCM showed that the participants in both ACT conditions reported fewer psychiatric symptoms in the areas of thought disorder and unusual activity, as measured on the Brief Psychiatric Rating Scale (BPRS), than those receiving broker case‐management services (Morse et al., 1997). However, no significant between‐group differences were found on anxiety‐depression, hostility‐suspicion, or self‐esteem scales (Morse et al., 1997). The mental‐health outcomes did not differ in an updated trial (Kenny et al., 2004). In contrast, in a 12‐month ACT intervention for homeless persons with mental illness, there were significant reductions (p < .001) in psychiatric symptoms using the Colorado Symptom Index (CSI) at 3 months (mean 4.10 (SEM 0.10) versus 3.61 (SEM 0.10), 6 months (mean 4.10 (SEM0.10) versus 3.61 (SEM 0.10) and 12 months (Mean 4.12 (SEM0.11) versus 3.77 (SEM0.11) in the ACT group, respectively, compared to the TAU group (p = .03) (Lehman et al., 1997). Another 18‐month ACT intervention versus SCM for homeless clients who were high service users with serious mental disorders reported significant improvement (lower symptom levels) in psychoticism subscales with time (p < .01) in the ACT groups than the SCM groups (Essock et al., 1998). Finally, a 3‐year ACT intervention (n = 99) with SCM (n = 99) reported no significant between‐group differences favouring the ACT group over the SCM in reductions in the severity of psychiatric symptoms, using the Expanded Brief Psychiatric Rating Scale (Essock et al., 2006).

Outcome 3: Quality of life

Three trials reported on the impact of ACT intervention on quality of life (Essock et al., 1998; Essock et al., 2006; Lehman et al., 1997). Lehman (1997) ACT trial (n = 77) reported improvements in the quality of life subscales at 6 and 12 months, respectively. The participants in the ACT programme compared to the TAU group were more satisfied with their general well‐being (ACT mean 4.70, SEM 0.16 vs. comparison mean 4.17, SEM 0.16, p = .02), neighbourhoods (ACT—mean 4.89, SEM 0.16 vs control mean 4.13, SEM 0.16, p = .001), and health (ACT mean 4.98, SEM 0.12 vs. comparison mean 4.50, SEM 0.12, p = .006). However, there were no between‐group differences in participants' objective quality of life or in most life‐satisfaction subscales (except for general well‐being and neighbourhood) (Lehman et al., 1997). Another ACT trial reported significant improvements in general life satisfaction (from 4.34 to 5.07) in participants in the ACT group compared to the SCM group (from 4.62 to 4.61) (p < .05) (Essock et al., 1998). A follow‐up trial reported no statistically significant between‐group differences observed in the participants' quality of life (Essock et al., 2006).

Outcome 4: Substance use

Five RCTs and a follow‐up study on different ACT interventions reported findings on substance‐use outcomes (Essock et al., 2006; Fletcher et al., 2008; Morse et al., 1992, 1997, 2006). In three RCTs, no major reductions were reported in substance‐use ratings, days of substance/alcohol use or alcohol consumption at 6‐ to 24‐month periods (Morse et al., 2006, 2008; Fletcher et al., 2008). One 12‐month three‐arm trial of ACT, a drop‐in centre and outpatient treatment reported more ounces of alcohol consumption—2.83 ounces (SD 9.11) in the ACT group compared to 0.50 (SD 1.08) and 0.95 (SD 1.98) ounces in the drop‐in centre group and the outpatient clinic group, respectively. There was no significant improvement in alcohol consumption over time (p = .781) (Morse et al., 1992). Another three‐arm trial reported no significant positive effect between the ACT (O) and the Broker CM interventions on the self‐esteem score, the client‐ or interviewer‐rated need for alcohol or drug treatment, or days of substance abuse at 18 months, using the addiction severity index (Morse et al., 1997). Another three‐arm trial found some improvements in substance use, with ratings assessed at 6, 12, 18 and 24 months. The mean substance‐use ratings for the ACTO and IACT participants were 2.70 (SD 1.28) and 2.76 (SD 1.11) compared to a score of 2.62 (1.15) in the control group, at 24 months (Morse et al., 2006). Even though participants receiving interventions reported improvements over time in substance‐use outcomes, no significant difference between treatment groups (p = .72) was observed (Morse et al., 2006). A follow‐up study compared previously published substance‐use ratings data for ACTO, IACT and standard care with new integrated assertive community treatment (NIACT) found that clients in the NIACT condition had reduced their frequency of drug use more than clients in the IACT and ACTO conditions (Morse et al., 2008). One trial found significant differences in the alcohol‐, drug‐ and substance‐use and substance‐abuse scales (p < .01, p < .0, p < .05 and p < .05) between ACT and SCM over a 3‐year period (Essock et al., 1998). Another three‐arm ACT intervention reported that the mean substance‐use rating was 2.58 (SD 1.11) and 2.73 (SD 1.25) for the ACTO and IACT groups, whereas the control group had a rating of 2.44 (1.20) (Fletcher et al., 2008). All groups improved over time; however, there were no significant differences between treatment groups. An ACT trial in two urban sites reported a score of 3 or higher for the AUS at baseline, and clients with alcohol‐use disorder showed no difference over time according to the researcher's average Alcohol Use Scale (AUS) ratings but they differed significantly over time on their self‐reported days of drinking (Essock et al., 2006). Using the drug‐use scales, with a baseline score of 3 or higher, a greater between‐group difference over time favouring ACT was observed at site 2 but not at site 1 (Essock et al., 2006). However, the groups did not differ in self‐reported days of drug use but their reported days of use declined by about one‐third overall (Essock et al., 2006). However, in site 1, the treatment groups showed steady and similar improvement over time when assessed with the Substance Abuse Treatment Scale (SATS), whereas in site 2, the ACT group showed more rapid improvement than the SCM group but there were no significant differences between groups (Essock et al., 2006).

Outcome 5: Hospitalisation

Four ACT trials reported on hospitalisation outcomes (Clarke et al., 2000; Essock et al., 1998, 2006; Lehman et al., 1997). One 24‐month RCT trial reported that slightly more ACT clients (46%) were hospitalised compared to 40% of those in usual care (OR, 1.22; 95% CI, 0.62–2.4) at 24 months, whereas 35% of the ACT clients (n = 40/114) visited the ER compared to 31% in the usual care group (n = 15/49) (OR, 1.23; 95% CI, 0.6–2.51) in the same period (Clarke et al., 2000). However, there were no significant between‐group differences in the number of hospitalisations or ER visits. In contrast, a trial reported marginal differences in hospital utilisation (p = .078) between ACT versus SCM clients after 18 months; however, the number of days hospitalised between 6 and 12 months was significantly higher for SCM clients (mean—25.8 days (SD = 57.1)) versus 17.2 days (SD = 46.9) (p < .05) for the ACT clients (Essock et al., 1998). Also, the ACT clients were not discharged from hospital more quickly (51 discharged clients) than those assigned to SCM, with 46 discharged within 18 months (Essock et al., 1998). A similar trial reported a slightly lower number of days hospitalised in the ACT group (mean 32, SD 91) than the SCM group (mean 41, SD 60) but this was not significant (Essock et al., 2006). Finally, one trial reported a significantly lower mean number of emergency department visits over 12 months (p = .005) in the ACT groups (mean 0.8 visits, SEM0.3) compared to UC (mean 2.0 visits, SEM0.3) (Lehman et al., 1997).

Outcome 6: Employment

No RCTs were reported on the effects of ACT on employment.

Outcome 7: Income

Only two trials reported evidence on the effects of different ACT interventions on participants' incomes (Morse et al., 1992, 1997). One three‐arm trial of ACT interventions—continuous community‐based services with a no‐reject policy, a drop‐in centre, and usual care (outpatient treatment) found no significant between‐group differences on participants' income outcomes (Morse et al., 1992). Also, another 18‐month trial comparing ACT groups with broker case‐management groups reported no significant between‐group differences associated with their income outcomes (Morse et al., 1997).

ICM Interventions

Thirteen RCTs and one nonrandomised trial that compared intensive case‐management intervention with the usual care or service, SCM and other services were included in this study.

Outcome 1: Housing stability

Thirteen trials and one nonrandomised trial on different ICM interventions reported evidence on housing outcomes (Braucht, 1995; Burnam, 1995; Conrad et al., 1998; Grace & Gill, 2014; Felton et al., 1995; Korr & Joseph, 1996; Malte et al., 2017; Marshall et al., 1995; Orwin et al., 1994; Toro et al., 1997; Rosenblum et al., 2002; Shern et al., 2000; Shumway et al., 2008; Stahler et al., 1995). One 24‐month trial of ICM interventions (n = 289) focused on long‐term, open‐ended, outreach‐oriented service that focused primarily on system advocacy and linkage activities in homeless and chronic inebriate clients reported significantly reduced mean number of days homeless in the last 60 days at 6, 12 and 18 months (p = .0013, p = .0007 and p = .0075) respectively, for the ICM participants (Cox et al., 1998). Also, there was a notable short‐term increase in the mean number of days in stable housing (p= .0072) in the ICM clients (Cox et al., 1998). Another RCT on a Demonstration Employment Project—Training and Housing (DEPTH) for mentally ill homeless adults with children reported reductions in the mean number of days homeless at 12 and 18 months in the ICM groups, but this was not significant (Toro et al., 1997). However, a significantly higher proportion of ICM participants (75.0%) were housed at 6 months compared to 34.1% of those in the UC group (OR 6.40 [2.61–15.68; p < .0001) (Toro et al., 1997). Another intensive client‐centred case‐management trial (n = 235) in unemployed and homeless youth reported a higher mean number of residence moves at 12 months in the ICM groups [2.2 more moves (SD 1.9) than the UC groups [1.8 moves (SD 1.9)], an effect that was reversed at 24 months (Grace & Gill, 2014). Also, the trial observed a lower mean number of days in no‐rent/privately rented accommodations observed at 12 and 24 months for the ICM intervention group but this was not statistically significant. Furthermore, a pooled analysis of three trials on ICM versus TAU reported some reductions in the number of days individuals spent homeless in the short term; that is, 7–12 months (SMD, −0.22; 95% CI, −0.49–0.05), but participants in the ICM programme showed significant reductions in the number of days homeless (SMD, −0.22; 95% CI, −0.40 to −0.03) after 13 months (Cox et al., 1998, Grace & Gill, 2014, Toro et al., 1997). The total overall effect: Z = 2.33 at p = .02. The interventions favour the use of ICM over TAU. Also, a 4‐months quasi‐experimental ICM trial on homeless substance users (n = 250) reported that improvements in the number of days homeless in the last 30 days was 13.2 versus 10.2 days for the ICM and TAU groups, respectively, but no significant between‐group difference was found even at 80% follow‐up (Rosenblum et al., 2002). Another 6‐month ICM trial on homeless mentally ill adults aged 18 years or older found that over twice as many (n = 36, 75%) ICM participants were housed than in the control group (n = 15, 34.1%) (Korr & Joseph, 1996). Clients receiving ICM were 5.8 times more likely to be housed (OR = 5.8; 95% CI, 2.35–14.31) than the control at follow‐up (OR = 6.40 at p < .0001) (Korr & Joseph, 1996). In a 14‐months ICM trial with homeless individuals with severe psychiatric disorders, for the ICM participants, there were no significant differences between groups in days in better or worse accommodations. The ICM groups had more days in better accommodation (mean: 44.3 days) than in the control group (mean 32.3 days) and fewer days in worse accommodation than the control (mean 15.1 vs. 33.4 days) (Marshall et al., 1995). Still, a three‐arm ICM trial with ICM for homeless persons with alcohol‐ or drug‐use problems reported that fewer ICM clients 58 (0.34) achieved housing independence than the control group 100 (0.48) clients; also, an effect size of −0.28 favoured the control condition (Orwin et al., 1994). A 24‐month ICM programme for street‐dwelling individuals with psychiatric disabilities reported that participants spent significantly more time in community housing (MD 11.07, t = 2.28 at p = .023) and shelters (MD 20.29, t = 5.48 at p < .0001) and significantly less time on the streets (MD −26.71, t = −4.25 at p < .0001) (Shern et al., 2000). However, there was no significant difference between time spent in institutions in both the ICM and TAU groups (MD −2.33) (Shern et al., 2000). Amongst predominantly male and unmarried homeless veterans enroled in addiction treatment and exposed to ICM interventions, there were no statistically significant differences in housing stability in both the intervention and control groups (Malte et al., 2017). Another 6‐month three‐arm ICM trial for adult males experiencing homelessness with alcohol and/or drug problems and stable mental health reported some improvements in housing stability, but there were no statistically significant between‐group differences (Stahler et al., 1995). Also, an earlier three‐arm trial for homeless adults with both serious mental illness and substance dependence reported no significant difference in the percentage of time spent on the streets between the residential and nonresidential groups or between both treatment groups and the control over a 9‐month follow up (Burnam 1995); and another 10‐month trial reported no significant difference between ICM and TAU on housing stability (Braucht 1995). Finally, a 24‐month ICM intervention on the homeless or vulnerably housed who were frequent emergency department users with psychological problems reported significantly lower levels of homelessness in patients who were randomised to the case‐management condition (Shumway et al., 2008).

Outcome 2: Mental health

Twelve studies on ICM interventions reported evidence on the mental‐health outcomes (Braucht, 1995; Burnam, 1995; Clark & Rich, 2003; Cauce, 1994; Felton et al., 1995; Malte et al., 2017; Marshall et al., 1995; Orwin et al., 1994; Shern et al., 2000; Shumway et al., 2008; Stahler et al., 1995; Toro et al., 1997). A three‐arm ICM trial on homeless individuals, long‐term psychiatric inpatients, and heavy users of emergency services with serious and persistent mental illness reported no significant differences between groups (Felton et al., 1995). Another three‐arm ICM trial on homeless persons reported lower improvements in 30‐day psychiatric symptoms (0.03) compared to 0.15 in improvements in the control group measured according to the Addiction Severity Index (ASI) (Orwin et al., 1994). In contrast, the improvement rate in the psychiatric composite score was 0.15 for the ICM group and 0.21 for the control group; however, there was no statistically significant difference between these groups (Orwin et al., 1994). Another 3‐month ICM trial with homeless adolescents between 13 and 21 years old reported slight reductions in youth self‐reports of depression problems according to the Reynolds Adolescent Depression Scale (RADS) (MD: −3.70; t = −1.33 at p = .18); and in total behavioural problems (MD: −0.50; t = −0.27 at p = .78) in the ICM group; however, no improvement was found in the antisocial behaviour (MD: 0.20; t = 1.26 at p = .20) as measured using the Problem Behaviour Scale (PBS) (Cauce 1994).

Also, a randomised ICM trial for homelessness with alcohol and/or drug problems and stable mental health reported effects on the number of days experiencing psychological symptoms in the last 30 days, using the ASI, found slight improvements in mental health (Stahler et al., 1995). There were no notable changes in participants' self‐esteem or mastery scores or these youth's self‐reports on depression, antisocial behaviour, their Problem Behaviour Scale (PBS), or the group's total behavioural problems (Stahler et al., 1995).

In one 14 month trial, ICM clients who were compared to TAU clients were assessed for the frequency of items of embarrassing or disruptive behaviours, using the REHAB standardised behaviour scale showed better outcomes on three of the five variables (REHAB general and deviant behaviours and mental state) but only deviant behaviour differed significantly between the two groups (MD, 0.3; 95% CI, 0.15–0.46) (Marshall et al., 1995). There was no significant difference in the severity of psychiatric symptoms. However, there was a significant reduction (mean = 0.79; 95% CI, 0.26–1.32; p = .0038) in psychological symptoms (deviant behaviours) from the baseline between the ICM and UC groups, using a standardised behaviour‐rating scale (REHAB) (Marshall et al., 1995). Also, another 18‐month ICM trial with mentally ill homeless adults with children reported psychological symptoms measured at 6, 12 and 18 months (Toro et al., 1997). When using the SCL‐90‐R checklist, significant reductions in psychiatric symptoms (MD −0.19; p = .04) were found between the ICM and UC groups, and the mean MLEI score on stressful life events was MD: −2.10 (p = .04) at 18 months (Toro et al., 1997). There were no significant differences in the psychological symptoms, as measured with the SCL‐90‐R, across time or groups (Toro et al., 1997). A 24‐month ICM ‐based intervention (“Choices”) compared to TAU reported significantly greater reductions in anxiety, depression, and thought disturbances in the experimental group (t = 2.41, p < .001), as measured with Colorado Symptom Index (CSI), compared to the control group (Shern et al., 2000). In a quasi‐experimental trial of a comprehensive housing programme compared with case management for homeless adults with mental illness (n = 152) Clark & Rich, 2003 found no significant differences between treatment groups for low and medium impairments. Also, patients randomised to the case‐management condition in the ICM intervention for homeless or vulnerably housed frequent emergency department users (n = 252) found no statistically significant differences for psychiatric symptoms (Shumway et al., 2008). Another 12‐month ICM intervention (n = 91) versus a drop‐in housing support group (n = 90) for homeless veterans enroled in addictions treatment reported greater improvements in the ASI alcohol composite score in the ICM group compared to those in the control group, but this was not statistically significant (Malte et al., 2017). Also, there were no significant differences between the two groups in mental‐health outcomes as measured by the ASI Psychiatric or the SF‐36 MCS at 12 months follow up.

Outcome 3: Quality of life

Five included studies assessed the effects of different ICM interventions on quality of life outcomes (Braucht 1995; Cauce 1994; Felton et al., 1995; Marshall et al., 1995; Shern et al., 2000). A 3‐month ICM intervention study on homeless adolescents 13–21 years old reported = slight improvements in quality of life, using the Life Domains Scale (LDS): a mean score of 3.6 (SD 0.8) compared to the control group 3.5 (SD 0.7). The study also reported self‐esteem, using the Rosenberg Self‐Esteem Scale (RSES): mean score 1.7 (SD 1.7) compared to the control group 1.6 (SD 1.6) (Cauce 1994). Another 14‐month RCT on ICM interventions for homeless persons reported no improvements in quality‐of‐life outcomes (MD, 0.0; 95% CI, −0.42–0.42) (Marshall et al., 1995). Also, a three‐arm ICM intervention on homeless individuals found significant linear group‐by‐time interactions for satisfaction with living situations and finances as well as fewer life problems, as measured by sub scores (Felton et al., 1995). In contrast, a 10‐month trial assessing the effects of ICM reported better improvements in general life satisfaction in the control group than in the ICM group (Braucht 1995). Finally, a 24‐month ICM (“Choices”) versus TAU trial reported between‐group differences in life satisfaction across 7 life areas (Shern et al., 2000). Individuals in the experimental condition reported consistently greater improvements in life satisfaction than their peers in the control group, in 6 of the 7 life areas: overall life satisfaction (p = .001); leisure (p = .027); financial (p = .001); safety (p = .005); health (p = .006); family (p = .005); and social (p = .56) (Shern et al., 2000). In most cases, experimental groups showed substantial gains, which were often 0.5 SDs more than observed in the control group (Shern et al., 2000).

Outcome 4: Substance use

Ten ICM trials reported evidence on substance‐use outcomes (Cauce 1994; Cox et al., 1998; Braucht 1995; Burnam 1995; Felton et al., 1995; Malte et al., 2017; Orwin et al., 1994; Rosenblum et al., 2002; Shumway et al., 2008; Stahler et al., 1995; Toro et al., 1997). A 24‐month three‐arm ICM intervention reported a lower improvement rate of 0.19 ((P<0.05) in alcohol use over 30 days, as assessed by the ASI scale for ICM participants compared to 0.40 rate condition (Orwin et al., 1994). Also, the mean number of drug‐use days was higher in the ICM groups (3.3 days) than in the TAU groups (1.51 days). However, there were no significant differences in the mean alcohol use in the past 30 days and the composite alcohol‐ or drug‐use scores (Orwin et al., 1994). Another ICM trial (n = 289) on the substance use outcomes of homeless chronic inebriate clients reported lower numbers of days of alcohol use in the past 30 days at 18 months in the ICM interventions compared to the UC group (MD −4.00, t = −2.31 at p = .02) (Cox et al., 1998). Also, the number of days of alcohol use in the past 30 days to the point of feeling the effects was lower in the ICM groups at 6 months (MD: −3.40; p = .05) (Cox et al., 1998). The number of days of alcohol use since the last interview were significantly lower at 6, 12, 18 months in the ICM groups ‐: MD: −21.00, −19.00 and −29.00 at p = .02, p = .04 and p = .001, respectively. While the number of detoxification centre admissions was reduced as the interventions moved from short (6 or 12 months) to long term (18 months); however, this was not statistically significant (Cox et al., 1998). Furthermore, ratings on how troubled or bothered subjects were by alcohol were lower in the ICM groups compared to the UC groups at 18 months (t = −2.29 at p = .02) than at 6‐ or 12‐months as well, the composite score for alcohol use on the Addiction Severity Index (ASI) was significantly lower in the ICM group compared to the control at 6 months (t = −1.94; p = .05), but not at 12 or 18 months (Cox et al., 1998). Another 18‐month ICM intervention (n = 202) reported no significant differences between groups across time in the number of drinks consumed daily over the course of the past year, using an author‐developed alcohol‐drinking index (Toro et al., 1997). However, a 4‐month study reported substantial reductions between ICM and UC groups in crack use in the past 30 days: 4.1 vs. 2.2 days (MD: −1.9; p < .05) (Rosenblum et al., 2002). A 9‐months trial of a shelter‐based intensive case‐management programme staffed primarily by peer counsellors versus regular shelter services provided by city‐staffed case managers found no significant differences in substance use, assessed using the Addiction Severity Index (ASI) (Stahler et al., 1995). However, in another trial, recent alcohol and cocaine use across the groups from the baseline significantly improved (p<0.05) at 18 months (Toro et al., 1997). A 3‐month ICM trial for youth measured substance use with a Personal Experience Screening Questionnaire (PESQ) and reported mean scores of 25.4 (SD 8.9) and 27.0 (SD 9.7) for the ICM and control groups, respectively, but no significant differences between groups (Cauce 1994). Also, a 10‐month ICM intervention reported little to no significant effects on substance use between ICM and TAU (Braucht 1995), while another three‐arm ICM trial did not observe significant differences in substance use in the past 30 days (days using alcohol, level‐alcohol use, days using drugs or severity of drug use) between all groups(Burnam 1995). Also, patients in the ICM condition showed reduced problematic substance use compared to the control group after 24 months (Shumway et al., 2008), and ICM participants (n = 91), in contrast to a drop‐in housing support group (n = 90), showed greater improvements in the ASI alcohol composite score. However, there was no significant between‐group differences in the proportion of participants who had abstained from alcohol or drug use (Malte et al., 2017).

Outcome 5: Hospitalisation

Five trials reported evidence on hospitalisation outcomes (Korr & Joseph, 1996; Malte et al., 2017; Marshall et al., 1995; Rosenblum et al., 2002; Shumway et al., 2008). A 14‐month ICM trial for homeless individuals with severe and persistent psychiatric disorders reported slightly fewer days in hospital (mean14.6; SD 30.5) for the intervention group than in the control group (mean 21.8; SD 62.3) (Marshall et al., 1995). Also, another 4‐month ICM trial reported significantly fewer hospital emergency‐room visits in the ICM group compared to the control group (26% vs. 45%; p < .05) (Rosenblum et al., 2002). In addition, a 24‐month ICM trial consisting of homeless or vulnerably housed who were frequent emergency‐department users reported significantly lower levels of hospital emergency‐rooms visits in ICM participants compared to the control group (Shumway et al., 2008). However, a 12‐month trial reported no significant between‐group differences in the number of days in hospital after adjusting for hospital days during the baseline period (Malte et al., 2017), and another 6‐month ICM intervention for homeless mentally ill adults aged 18 or older found no statistically significant difference between groups on the number of days in hospital (Korr & Joseph, 1996).

Outcome 6: Employment

A 10‐month (ICM) trial (n = 178) that consisted of homeless individuals (18 years or older) with alcohol or other substance‐abuse problems found nonsignificant effects on employment outcomes (Braucht 1995). Also, a 2‐year ICM trial with homeless chronic inebriate clients (n = 150) reported no significant between‐group differences in employment outcomes compared to the standard‐care group (Cox et al., 1998). Although a 14‐month ICM trial on homeless individuals with severe and persistent psychiatric disorders reported that the ICM participants spent more days in any employment than those in the control group, the effect was not significant (Marshall et al., 1995). Another 24‐month three‐arm ICM trial found significantly better improvements in employment outcomes compared to the usual or episodic care of those in the intervention group; however, the report highlighted the data‐analysis procedures as not accurately described (Orwin et al., 1994). Finally, a 6‐month three‐arm ICM trial that consisted of adult males experiencing homelessness with alcohol and/or drug problems and who had stable mental health reported slight improvements in employment outcomes, but the between‐group differences were not statistically significant (Stahler et al., 1995).

Outcome 7: Income

Five trials reported on evidence of ICM interventions on participants' income (Cox et al., 1998; Grace & Gill, 2014; Rosenblum et al., 2002; Shumway et al., 2008; Toro et al., 1997). A 24‐month ICM intervention that included monthly public income assistance for homeless chronic inebriate clients (n = 150) found a significant group effect favouring the ICM group over those in the standard‐care group (n = 148) (Cox et al., 1998). A 24‐month nonRCT of intensive client‐centred case management that provided a range of brokered services through a single point of contact (YP case manager) to unemployed and homeless young people (n = 422) found no statistically significant between‐group differences in higher receipts of public income assistance in the ICM group than in the control group (Rosenblum et al., 2002). Another 24‐month trial reported that the patient population of homeless or vulnerably housed, frequent emergency‐department users with psychological problems and randomised to the case‐management condition showed significantly lower levels of unmet financial needs than those in the usual care (Shumway et al., 2008). Finally, an 18‐month ICM trial that consisted of mentally ill homeless adults with children (n = 202) found no statistically significant differences in effects on income outcomes between groups (Toro et al., 1997).

Critical time intervention

Our systematic review yielded 5 studies (11 citations) on CTI (De Vet, 2017; Herman et al., 2011; Lako et al., 2018; Susser et al., 1997; Shinn et al., 2015). One study (2 citations) specifically explored family critical time intervention (FCTI), a multidisciplinary community‐based service model targeted towards families, that connects families with social services and forms supportive relationships with families and friends during critical times of transition from shelters to community housing (Shinn et al., 2015).

In all studies, CTI consisted of three phases. This was primarily broken down into (1) transition to the community, (2) tryout, and (3) transfer of care. One study (Susser et al., 1997) described these phases as (1) accommodation, (2) try out, and (3) termination. All trials compared the intervention to the TAU, though the scope of the interventions associated with usual care somewhat differed between trials. Between the five studies, follow up ranged from 9 to 24 months. All studies were RCTs; two were based in the Netherlands (de Vet 2017; Lako et al., 2018) and three were from the United States (Herman et al., 2011; Susser et al., 1997; Shinn et al., 2015).

Outcome 1: Housing stability

Three out of four studies found that CTI significantly reduced the number of days spent homeless (Herman et al., 2011; Susser et al., 1997; Shinn et al., 2015). Two studies reported on the total number of homeless nights experienced in an 18 month follow‐up period (Herman et al., 2011; Susser et al., 1997). In both studies, the participants in the CTI group received 9 months of CTI plus usual services and then usual services only for the following 9 months, while the participants in the TAU group received a total of 18 months of usual services only (Herman et al., 2011; Susser et al., 1997). In both studies, usual care was a mix of various types of case management and clinical treatment. Within Herman et al. (2011), all participants in both treatment arms also received basic discharge‐planning services and access to psychiatric treatment while living in the transitional residence. Herman et al., 2011 found that over an 18‐month period in persons with severe mental illness discharged from New York City inpatient psychiatric‐treatment facilities (n= 150), there were 1812 total homeless nights in the CTI group compared to 2,403 homeless nights in the control group (p < .001). Controlling for baseline homelessness, the OR for the CTI group was 0.28 (95% CI, 0.78 to −1.02), suggesting that the CTI group had a 5‐fold reduction in risk of homelessness within the intent‐to‐treat analysis. Similarly, Susser et al. (1997) examined 96 men with severe mental illness who had been discharged from an NYC men's shelter's on‐site psychiatric programme to return to community housing. The number of homeless nights over the 18‐month follow up period was also statistically significant, with 1415 homeless nights in the CTI group and 4,370 in the TAU group. The risk of a major homeless episode was significantly lower in the CTI than in the usual‐services group (p = .003) and the survival curves comparing the differences between major homeless episodes between both groups widened over the duration of the study.

Susser et al. (1997) subsequently divided homelessness into extended homelessness (more than 54 nights), intermediate homelessness (30–54 nights), and transient homelessness (1–29 nights). There was a significantly reduced amount of extended homelessness in the CTI group (X ² = 4.0, df = 1, p = .045), with a relative risk of 0.53 (95% CI Taylor series, 0.27–1.01). There was no significant difference between episodes of intermediate homelessness and transient homelessness.

In examining time spent in conventional housing, Shinn et al. (2015) studied 200 newly homeless families in which mothers had diagnosable mental illness or substance‐use problems. They found that, after random assignment, families in the FCTI treatment group spent 43% of the first 3 months and 91% of the next 6 months in conventional housing in the community, compared to 8 and 45% for families in the usual‐care control group. The FCTI services ended at 9 months. Families in the FCTI group spent 89% of the time from 9 to 15 months and 86% of the time from 15 to 24 months in community housing, compared to 76 and 73%, respectively, in the control group.

FCTI may also reduce transition time from a shelter to community housing. A longitudinal RCT (n = 210) examined homeless mothers with a mental illness/substance‐abuse disorder as they moved from homeless shelters into affordable housing (Samuels et al., 2015). Families in the FCTI intervention group were not required to meet specific housing‐readiness criteria, compared to the control group. Hence, a higher number of FCTI families left the shelter (98%) compared to the control group (84%) and the average number of days until they moved into stable housing was significantly reduced, at 91.25 (SD 82.3) days compared to the control group average of 199.15 days (SD 124.4). Over the course of the study, the control group became significantly less likely to spend a longer period in the shelter than the intervention group. Because of the early success of the FCTI in rehousing families in a timely manner, county officials increased the availability of permanent‐housing vouchers to families involved in the homeless service system, enabling families in the control condition to also receive housing more quickly.

One trial, based out of the Netherlands, did not find a significant difference in the number of days rehoused with CTI versus TAU (de Vet, 2017). The number of days re‐housed was defined as living in conventional independent housing; i.e., property or legal (sub) tenancy, or accommodation permanently provided by relatives, friends or acquaintances. The Residential Follow‐Back Calendar was used to assess participants' residential history in this multicentre parallel‐group RCT.

Outcome 2: Mental health

In two studies, there were no significant differences in levels of psychological distress between CTI versus TAU, as measured using the Global Severity Index, which provides an average score of a 53‐item symptom inventory (de Vet, 2017; Lako et al., 2018). However, a longitudinal RCT by Samuels et al. (2015) (n = 210) examined the effect of FCTI on homeless mothers with mental illness and found that both the FCTI and the usual services resulted in improvements in these mothers' mental‐health problems over time, even if there were no significant differences between the intervention and control groups. The Global Severity Index was also used to assess mental health in this study, with data from nine primary‐symptom sub‐scales of the Brief Symptom Inventory: psychopathology, including somatisation, obsessive‐compulsive, interpersonal sensitivity, depression, anxiety, hostility; phobic anxiety; paranoid ideation; and psychoticism. At baseline, the mothers in the study had relatively high levels of mental‐health symptoms, with the mean standard score for the GSI falling close to the borderline problem range (M = 57.7; SD = 12). Between the baseline and the 15‐month assessment, the GSI scores dropped by an average of 9 points, bringing most mothers into the normal range of mental health relative to the general adult population. The mean score for those in the top 25th percentile at baseline was t = 66, dropping to t = 59 at 15 months. The mean score for mothers in the lowest 25th percentile dropped from t = 50 to t = 33. Both the control and intervention groups experienced similar improvements in symptoms over time, with the elevated symptoms in mothers in the treatment group declining from 77% at the baseline to 42% at the 9‐month follow up, and the percentages in the control condition declining from 73% to 38%, respectively.

In one of these studies—a multicentre RCT in the Netherlands that examined 183 adults who were moving from shelters to supported or independent housing— the CTI had an added differential effect on psychological distress for participants who were experiencing less social support, with an estimated difference in the intervention effect = 0.19 (p = .013, 95% CI, 0.004–0.34) suggesting that a CTI may provide more benefit to less supported individuals (de Vet, 2017).

Two studies measured self‐esteem, using the 10‐item Rosenberg Self Esteem scale, and found no difference with the CTI intervention (de Vet, 2017; Lako et al., 2018). In one study, there was also no impact on depression as measured with the 20‐item Centre for Epidemiological Studies Depression Scale (Lako et al., 2018). However, in the same study, CTI appeared to significantly improve symptoms of PTSD during follow up (adjusted MD, 7.27; 95% CI, −14.31 to −0.22, p = .04). The PTSD symptoms were measured by the sum score of the 15‐item Impact of Event scale (Lako et al., 2018 ). Further analysis revealed that the significant effect was primarily on non‐Dutch speaking women, compared to Dutch‐speaking women. No other studies examined the effect of CTI on PTSD.

CTI may also have a benefit for improving negative symptoms of schizophrenia. One RCT assessed 96 men with schizophrenia and other psychotic disorders who had been discharged from a homeless shelter (Herman et al., 2011). Symptom severity at the baseline and at 6 months was assessed using the Positive and Negative Symptom Scale (PANN), a 30‐item, 7‐point severity scale that is used to examine the three domains of positive symptoms, negative symptoms and general psychopathology. Data was collected from the 76 subjects for which there was a complete symptom set. The CTI was associated with significantly fewer negative symptoms, at the 6‐month follow up, defined as a cumulation of ratings of blunted affect, emotional withdrawal, poor rapport, passive‐apathetic social withdrawal, difficulty in abstract thinking, lack of spontaneity, and flow of conversation and stereotyped thinking. The mean change in the CTI group was −2.6, compared to a mean change of +1.0 in the usual treatment group. In the regression analysis that controlled for baseline score, in the 6‐month outcomes, there was a significant group effect for negative symptoms only (F = 6.7, p = .02). There was no significant effect on positive or general psychopathology symptoms.

Regarding the effect of FCTI on children, one RCT compared FCTI to usual care for children of 200 newly homeless families with maternal diagnosable mental illness or SUDs (Shinn et al., 2015). Mothers completed the Child behaviour Checklist, and youth ages 11–16 reported their own internalising and externalising behaviours using the Youth Self‐Report. Teachers reported externalising behaviours using the Teacher Report Form. The FCTI appeared to reduce internalising behaviours in children until 24 months when both groups had similar levels. The greatest difference between the 2 groups (0.6 SDs) was at 9 months. The FCTI also had an impact on externalising behaviours, with an improvement in group differences in T scores by 6.2 (0.5 SDs). There was also an improvement in 0.4 SDs in internalising and 0.2 in externalising for children aged 1.5–5 years. For children between 6 and 10 years, the intervention on mental health had no effect but both the CTI and usual‐care treatment groups showed significant improvements, over time, for mother‐reported internalising and externalising behaviours and child‐reported depressive symptoms. In adolescents aged 11–16 years, the FCTI group had a reduction in mother‐reported externalising behaviour that was not seen in the usual care group. At 24 months, the difference between these two groups was 6.2 (0.5 SDs). The children's self‐reports showed that there were no effects on externalising behaviours.

Outcome 3: Quality of life

Quality of life was assessed in two studies (de Vet, 2017; Lako et al., 2018). CTI was found to have no statistically significant impact on the quality of life in either study. Both studies used general questions on life satisfaction from Lehman's Brief Quality of Life Interview to assess quality of life. Both studies were based out of the Netherlands, were RCTs and had a 9‐month follow‐up period. In one study, there were also no significant differences in re‐abuse between groups, using the question, “[H]ave you been abused since the last interview?” The Impact of Event Scale (IES) at 9 months was lower in the CTI group (M 29.04) compared to care as usual (M 32.19), with a p value of .04 (de Vet, 2017).

Outcome 4: Substance use

One study examined the effect of CTI vs care as usual on substance use (de Vet, 2017). Excessive alcohol use (i.e., five or more drinks a day) or cannabis use in the past 30 days was assessed using the European Addiction Severity Index. The baseline characteristics between the CTI versus the control group differed, with a higher proportion of participants in the CTI reporting excessive alcohol use in the past 30 days (21%) compared to the control group (20%), with a p value of 0.04. At the 9‐month follow up, there was a trend towards reduced substance use in the CTI group, though it did not reach significance. Twenty‐two percent of participants in the CTI group reported excessive alcohol use compared to 26% in the control group, with an adjusted OR of 0.71, a 95% CI of 0.24–2.09. Cannabis use was reported in 15% of the CTI participants vs 23% in the control group, with an adjusted OR of 0.89 (95% CI, 0.26–3.05).

Outcome 5: Hospitalisation

A study by Tomita 2012 found that participants receiving CTI had significantly reduced odds of psychiatric re‐hospitalisations during the final three observation intervals (OR = 0.11; 95% CI, 0.01–0.96). The usual services and CTI groups had a total of 1508 and 1183 psychiatric re‐hospitalisation nights, respectively, during the final three intervals, with both the proportion (27% vs 18%, p < .05) and frequency of re‐hospitalisation nights above the median (49 vs. 31, p < .05) being significantly higher for the usual‐services group. Psychiatric re‐hospitalisation rates were higher in the usual‐services group during all intervals except one.

Outcome 6: Employment

No trials studied the effect of CTI on employment outcomes.

Outcome 7: Income

One trial showed that CTI had no significant impact on income‐related outcomes compared to usual services over an 18‐month study period (Susser et al., 1997).

Cost‐effectiveness studies

Permanent supportive housing

Fourteen studies performed a cost analysis of PSH interventions and reported mixed results regarding resource requirements. Seven studies showed that the PSH interventions were associated with increased cost to the payers and that the cost of the interventions were only partially offset by savings in medical‐ and social_services costs as a result of the intervention (Aubry et al., 2016; Culhane et al., 2002; Dickey et al., 1997; Gilmer et al., 2009, 2010; Mares & Rosenheck, 2011; Stergiopoulos et al., 2015). Six studies revealed that PSH interventions saved the payers money (Hunter et al., 2017; Larimer, 2009; Lenz‐Rashid, 2017; Chalmers McLaughlin, 2011; Schinka et al., 1998; Srebnik et al., 2013). However, some studies were based on a pre‐post design (Hunter et al., 2017; Lenz‐Rashid, 2017; Chalmers McLaughlin, 2011; Srebnik et al., 2013); therefore, estimated savings cannot be fully attributed to PSH. We identified three economic evaluations: the first study (Holtgrave et al., 2013) was a cost‐utility analysis of PSH which suggested that the provision of housing services was associated with increased costs and increased quality‐adjusted life years (QALY), with an incremental cost‐effectiveness ratio of US$62,493 per QALY. However, the methodological quality of this study was poor and lacked transparency, there were insufficient details on the design and the results of the effectiveness study, and no justification was given for the choice of mathematical model and the key parameters used. Another study concluded that, compared with usual care, PSH was more costly to society (C$7868, 95% CI 4409–11405) but it increased the number of days spent stably housed (140 days, 95% CI, 128–153) (Latimer et al., 2019). If the payer is willing to pay C$56 per 1 day of stable housing, then the PSH is considered cost‐effective.

Income assistance

Two studies focused on the cost‐effectiveness of income‐assistance interventions. Rosenheck and colleagues (Rosenheck et al., 2003) considered income‐assistance interventions in the form of rental assistance and showed that intervention clients had greater annual costs but fewer days homeless than the standard‐care and the case‐management‐only groups. For each additional day housed, clients who received income assistance incurred additional costs of US$58 (95% CI, $4–$111) from the perspective of VA, US$50 (95% CI, −$17, $117) from the perspective of the health‐care system, and US$45 (95% CI, −$19, −$108) from the societal perspective. In addition, the benefits gained from temporary financial assistance were found to outweigh the costs, with a net savings of US$20,548 (Evans et al., 2016). We did not identify any studies that reported the cost‐effectiveness of social‐assistance programmes and employment support.

SCM and mental health interventions

The economic implications of case‐management interventions (SCM, ICM, ACT, CTI) was highly uncertain. SCM clients were found to incur higher costs than those receiving the usual or standard care (Nyamathi et al., 2016; Shumway et al., 2008) and ACT (Clark et al., 1998; Essock et al., 1998) but lower compared to those receiving a US clinical case‐management programme that included housing vouchers and ICM (Rosenheck et al., 2003). If the cost‐effectiveness studies used a societal perspective and considered the benefits gained by and costs borne to all payers, then SCM did not offer good value for money compared to the ACT for persons with serious mental disorders or those with a concurrent SUD as SCM was more costly but led to more days in unstable housing (Essock et al., 1998) and poorer quality of life (Clark et al., 1998). For ICM, all included studies suggested that the intervention may be cost‐offset or cost‐effective. The Canadian study (Stergiopoulos et al., 2015) showed that the cost of supporting housing with ICM could be partially offset by the reduction in the use of emergency shelters and single‐room occupancy. Consistently, the US study reported that ICM was more likely to be cost‐effective when all of the costs and benefits to society were considered (Rosenheck et al., 2003). A pre‐post study showed that the ICM provided to high users of emergency departments resulted in net hospital cost‐savings of USD $132,726 (Okin et al., 2000). Regarding ACT, included studies that focused on individuals with severe mental illness or dual disorders consistently revealed that ACT interventions were dominant, meaning that they saved the payers money and improved health outcomes (i.e., reduced substance abuse, improved quality of life, resulted in a greater number of community days and a greater number of days in stable housing) than the usual care. (Clarke et al., 2000; Essock et al., 1998; Lehman et al., 1999; Morse et al., 2006; Wolff, 1997). We identified only one cost‐effectiveness study of CTI (Susser et al., 1997), which reported that the CTI was dominant. In other words, despite having comparable costs (US$52,574 vs. US$51,749), the CTI led to greater nonhomeless nights (508 vs. 450 nights) compared to the usual services provided to men with severe mental illness.

No studies reported on the costs, cost‐effectiveness or resource requirements of peer support, SCFs, MAPs, injectable antipsychotics and OAT interventions.

DISCUSSION

Summary of main results

Permanent supportive housing

The majority of studies found both significant short‐ and long‐term benefits of PSH on our primary outcome of housing stability, as compared to usual care. One study in Toronto, Canada, presented a long‐term analysis, with a median follow up of 5.4 years, and found that the number of days spent stably housed remained significantly higher within the PSH group (Stergiopoulos et al., 2019). Findings from this study suggest that, when provided with housing arrangements that are not contingent on abstinence and coupled with supportive services, individuals who had experienced homelessness were able to maintain lasting housing stability. Most study populations consisted of individuals with severe mental illness who were experiencing chronic homelessness, often with a high degree of comorbid substance use. Subgroup analyses revealed a similar benefit of PSH for both youth and adults over the age of 50, as well as within both high‐ and moderate‐needs populations, suggesting that PSH caters to different demographics and levels of needs among individuals with lived experience of homelessness (Aubry et al., 2016). There may also be a differential effect related to gender and substance use on housing stability, although the results were mixed and require further study. Future research should focus on examining the equity impact of PSH and how patient characteristics affect the magnitude of effect as it relates to housing stability (Welch et al., 2010). The housing‐intervention models studied included both single‐site models with on‐site support and scattered‐site models with portable support. Our review did not set out to determine the most effective housing model. Further research using a realist lens is mandated to explore the elements and characteristics of PSH that truly contribute to lasting housing stability. Nonetheless, our findings suggest that PSH initiatives can be adapted to different contexts and sites and remain effective in improving housing stability, within populations with a high burden of comorbid mental illness and substance use disorders.

Most studies (n = 5) found no benefit of PSH on mental health, though two studies found that mental‐health symptoms improved in both the PSH and TAU groups, despite there being no significant difference between groups (Tsemberis et al., 2004; Sadowski et al., 2009) Three studies found some improved mental‐health symptoms in the comparison group, as opposed to the group in supportive housing (Aubry et al., 2016; Cherner et al., 2017; Young et al., 2009). In one of these studies, both interventions similarly improved symptoms of psychoticism, depression, anxiety, obsessive‐compulsive disorder, interpersonal sensitivity and phobic anxiety, but greater improvements in somatisation, paranoid ideation and global mental‐health‐symptom severity were noted in the “Continuous Integrated System of Care (CCISC)” model, an intervention based out of a traditional substance‐abuse treatment agency (Young et al., 2009). Only one study compared hybrid approaches to housing, such as “parallel housing” (resembling supportive housing + ACT) and “integrated housing” (resembling the traditional model); in this study, those in the integrated‐housing model had less severe psychiatric symptoms during the 18 month follow‐up period (McHugo et al., 2004). Lack of benefit of PSH on mental health outcomes likely represents the complexity of mental illness in this population (Harvard Health Publishing, 2014; Winiarski et al., 2020). Improving health outcomes in persons with lived experience of homelessness therefore may require a multipronged approach, combining multiple evidence‐based interventions. In addition, independence and privacy achieved with PSH may affect social networks and reduce interaction (Cherner et al., 2017). Prior research has demonstrated a positive relationship between perceived social support and psychological health (Harandi et al., 2017) and hence the provision of PSH could result in slower improvements in mental health particularly in early stages (Cherner et al., 2017). Future qualitative research is required to further examine whether PSH is inferior to temporary housing arrangements in regards to social isolation and mental health functioning. Moreover, older homeless adults may have significantly higher improvements in mental health with PSH compared to adolescents, based on subgroup analyses, though further research is required in this area (Aubry et al., 2016). It is possible that this effect may be mediated by lower substance‐use rates in older adults compared to adolescents, due to correlations between substance use and poor mental health in prior research (Aubry et al., 2016).

The effects of PSH on quality of life were mixed, with multiple studies finding a benefit of PSH over TAU, while others favouring the comparison group. Within the two studies that favoured the comparison groups over PSH, improvements in quality of life were still demonstrated in both the intervention and comparator groups (Cherner et al., 2017; McHugo et al., 2004). In one of these studies, the authors suggested that greater improvements in nonhousing outcomes in the comparator group compared to the intervention group may be related to the selection of participants (Cherner et al., 2017). The second study examined hybrid models of housing (parallel vs integrated housing), thus, creating limitations in direct comparison (McHugo et al., 2004). PSH may benefit condition‐specific quality of life (for example, within subscales relating to leisure, living and safety and family), though this requires further exploration (Aubry et al., 2016). As well, previous research on the correlation between quality of life and mental health is limited (Hubley et al., 2014). Nonetheless, the homeless samples in all of our included studies have reported a long lasting struggle with chronic mental health conditions which, in turn, could have been the confounding factor behind the attenuated effect of PSH on quality of life. Interestingly, one study noted a strong association of satisfaction with life with personality (Goldfinger et al., 1999). The authors of this study postulated that satisfaction with life in general may be strongly influenced by one's overall personality, with only some variation in response to residential circumstances. Specific social circumstances informing expectations could be incorporated into future research to better understand these results (Goldfinger et al., 1999).

The effects of PSH on substance abuse were also mixed, though most studies found no difference in substance use with PSH compared to the usual care. Only one study found a benefit over the comparison group, though notably, it was a single‐site trial of a larger multicity study that found no significant difference between groups (Stergiopoulos et al., 2015). One study on homeless clients with problematic substance use found a benefit of the TAU group over the HF intervention, with regard to substantial or severe problems with drug use at 24 months (Cherner et al., 2017). However, the authors postulated that improvements in the comparison group over PSH may have been related to the study's participant selection. Individuals who continued to have difficulties with substance use, despite past substance‐use treatments, were prioritised for admission into the programme; these individuals may have required more intensive interventions than could be provided by the provision of PSH with ICM (Cherner et al., 2017).

Several studies found that PSH reduced emergency‐department visits and days spent hospitalised. Interestingly, one study noted that the Housing‐First (HF) intervention appeared most beneficial for individuals who were recruited from psychiatric hospitals, as compared to individuals recruited from the street, who showed overall fairly low and consistent levels of hospitalisations throughout the study (Tsemberis et al., 2004). Sadowski et al. (2009) identified several factors which may have facilitated the success of PSH in reducing hospitalisations in their study, including the creation of a city‐wide comprehensive and coordinated effort between clinicians, social workers, housing and advocacy groups to secure case management and housing for every participant. Further exploration of factors corresponding to the success of intervention may aid in continued success of PSH implementation and lasting effectiveness.

There were a minimal number of studies that examined the effects on income and employment. The At‐Home‐Chez Toi study found that, compared with the control group of moderate‐needs participants, the HF ICM participants actually had lower odds of obtaining employment (Aubry et al., 2016). Over time, the odds of obtaining employment in both the HF‐ICM and ACT groups improved, compared to the control group, but despite this, the rates of employment in the HF group never exceeded those of the control group. For the ACT high‐needs group, the odds of obtaining employment was not statistically significant compared to the control group. Notably, there were several limitations of this study, including removal of a significant number of participants employed at baseline (11 of 61) due to insufficient data, and a high rate of attrition in the control group. Nonetheless, based on the results, the authors hypothesised that HF may have an initial effect of de‐incentivize work in the moderate‐needs participants whose functional levels are higher. With longer follow up, it is possible that employment in the HF group could actually surpass that of the control. It is unclear from the current research whether this difference may be ameliorated with the integration of evidence‐based supported‐employment programmes (Aubry et al., 2016). Future qualitative research should explore this phenomenon to understand reasons for the trivial effect of PSH on employment. In one study, there were no statistically significant differences in income (Aubry et al., 2016).

Income assistance

Our current review provided some evidence on the effectiveness of income‐assistance intervention in association with broad‐gauged social services delivered to the homeless population in the context of mental health, social health, and healthcare utilisation. The effect of income‐assistance interventions appeared most significant on measures of housing stability, specifically in the format of rental subsidies (Rosenheck et al., 2003; Hurlburt et al., 1996; Pankratz et al., 2017; Wolitski 2009). One study that assessed the effects of CWT showed reduced odds of an episode of homeless in the study group (Kashner, 2002). The effect of financial‐empowerment education (Ferguson, 2018) and IPS programmes (Ferguson, 2018) on housing stability were assessed in limited quantities of studies that did not demonstrate significant findings. In terms of the effects on mental‐health status, rental subsidies for the homeless population with AIDS and homeless families with one child demonstrated benefits on their mental‐health status based on their self‐reported depression scores and psychological distress levels (Wolitski, 2009; Gubits et al., 2018), but the effect did not appear significant among homeless veterans with psychiatric or addiction disorders who received housing vouchers (Rosenheck et al., 2003; Rosenheck et al., 2003). An IPS programme was reported to be associated with less self‐reported depression and ADHD symptoms as well as higher scores on a self‐reported self‐esteem scale (Ferguson, 2018). However, programmes in financial empowerment and CWT did not show significant benefits on mental‐health status (Booshehri, 2017; Kashner, 2002).

The effect of income‐assistance interventions on quality of life, substance‐use conditions and hospitalisations were not consistent across eligible studies due to diverse intervention characteristics, participant profiles, and units of measure (Rosenheck et al., 2003; Ferguson, 2018; Pankratz et al., 2017). One study on a CWT programme for homeless veterans with substance dependence found that this approach was reported to immediately reduce the consumption of alcohol and drugs within the first 3 months as well as mean number of inpatient days in medicine wards but not in psychiatric wards (Kashner, 2002).

The effect of income‐assistance interventions on employment and income improvement was reported as insignificant or uncertain. The only significant improvement on employment outcomes associated with income‐assistance interventions was reported among the homeless individuals with mental illness who were receiving the IPS, compared to those under SCM (Poremski et al., 2015). Among the six eligible studies that assessed income outcomes, o none demonstrated an association between income‐assistance interventions and increased income at the end of the study period (Booshehri, 2017; Ferguson, 2018; Gubits et al., 2018; Pankratz et al., 2017; Poremski et al., 2015; Rosenheck et al., 2003). Further research is needed to clarify the role of income‐assistance interventions on the earned incomes of homeless populations.

Standard cases management and peer support interventions

Standard case management

Case‐management methods appeared to show some benefit in some of the health and social outcomes that were examined in this review. In varied cases and study conditions, SCM interventions significantly improved housing stability and reduced the odds of homelessness in homeless individuals (Conrad et al., 1998; Upshur et al., 2015; Towe et al., 2019). In contrast, some studies observed small but not significant improvements in housing outcomes with mixed effects and no significant differences between groups (Nyamathi et al., 2016; Hurlburt et al., 1996). Although the effectiveness of SCM interventions on housing outcomes varied by type, duration and the contextual conditions of those in the intervention groups, the SCM interventions had better outcomes among the programme graduates of the interventions, which underscores the fidelity to this type of intervention (Graham‐Jones et al., 2004; Upshur et al., 2015; Lapham et al., 1996). Generally, SCM interventions had mild effects on mental health by reducing the odds of depression, with very slight improvements in both psychological well‐being and psychiatric symptoms; however, the overall mental‐health status remained largely unaffected (Conrad et al., 1998; Nyamathi et al., 2001; Upshur et al., 2015; Weinreb et al., 2016). Similarly, SCM interventions had negligible or no effect on participants' quality of life or substance‐use outcomes, with some studies reporting even better improvements in the nonintervention groups (Conrad et al., 1998; Graham‐Jones et al., 2004; Nyamathi et al., 2001; Sosin et al., 1995; Upshur et al., 2015).

Peer support

Our systematic review yielded six studies that examined the effectiveness of peer‐support programmes. All studies were based in the United States but implemented heterogeneous approaches to providing their cohorts with peer‐support services. Two studies linked homeless individuals to peer‐support workers who matched their ethnicities (Corrigan et al., 2017; Nyamathi et al., 2001). Two trials examined peer‐support programmes that were delivered in conjunction with housing interventions (Ellison et al., 2020; Lapham et al., 1996). One trial examined a peer‐coaching programme delivered to homeless men who had been released from incarceration during a time of transition (Nyamathi et al., 2016), whereas one trial provided peer mentorship to homeless veterans seeking continuous primary care (Yoon et al., 2017).

Regardless of the nature and complexity of the peer‐support programmes that were delivered to individuals with lived experience of homelessness, our findings suggest that these interventions cannot stand alone as an approach to decreasing housing instability, alleviating the pressure of urgent health services, or assisting individuals in maintaining long‐term and proper substance‐use behaviours. Four trials examined housing stability and found no added benefits to peer‐support programmes, even when coupled with housing assistance. The reason behind this inappreciable benefit in housing stability is unclear but it could be attributed to the limited intensity and tenure of peer‐support programmes. A companion systematic review on PSH found that coupling housing programmes with more intensive supportive programmes, such as ACT or ICM, promoted long term housing stability (Aubry et al., 2020). Moreover, four trials examined substance‐use outcomes following the receipt of peer‐support programmes. Findings from these trials suggested preliminary benefits pertaining to days of substance use but that these benefits seemed to have been trivial in magnitude and to have attenuated with time. Understanding the reasons for this attenuated and inconsiderable effect requires using a realist lens to explore the programme specifics that contribute to such preliminary benefits.

Findings on mental health were mixed and polarised as one randomised controlled trial found that pairing homeless African Americans with ethnically matched peer‐support workers decreased their psychological distress and improved their overall mental‐health status (Corrigan et al., 2017). Nyamathi et al. (2001) (Nyamathi et al., 2001), however, reported that providing peer‐support services to homeless women was associated with harms pertaining to their depression and anxiety symptoms. This finding is suggestive, yet again, of a relationship between programme intensity and prospective effectiveness as a companion review found similar harms in anxiety and hostility associated with delivering SCM to homeless women (Ponka et al., 2020), whereas more intensive interventions showed promise in improving mental‐health outcomes (Ponka et al., 2020). Another explanation of these harmful effects could be linked to the nature of the relationship between peer supporters and individuals with current homelessness.

A systematic review of qualitative studies found that promoting trust is therapeutic and preferable in the context of delivering care to individuals with lived experience of homelessness (Magwood et al., 2019). More in‐depth research that explores the perceptions behind receiving support from peers is mandated. Moreover, only one randomised trial examined hospitalisation outcomes and found no significant decrease in hospitalisation rates or emergency‐department utilisation associated with receiving peer‐support services (Yoon et al., 2017). More research is needed to explore health‐service utilisation, in the context of receiving peer support, before a more conclusive decision on its benefit could be put forward.

Mental health Interventions

Our analyses allowed us to comprehensively examine the effectiveness of a myriad of interventions and explore which carry the potential to improve the housing, health, and social statuses of individuals with lived experience of homelessness. Our findings suggest that more ICM programmes, such as ACT, ICM, and CTIs, carry the potential to improve housing outcomes. When examining mental health, quality of life, and substance use, evidence showed heterogeneous results as the majority of interventions contributed little to no improvements to these outcomes. Nonetheless, CTIs, as well as PSH coupled with ICM support, showed promise in reducing hospitalisations and emergency‐department utilisations. Finally, across all interventions, evidence on employment and income was scarce and nonsignificant, indicating the need for more trials to examine these financial‐related outcomes.

Intensive case management

ICM had a moderately significant positive effect on the housing stability of homeless persons, with evidence of immediate significant reductions in the number of days homeless as well as increased likelihood of being housed, by a magnitude of 5.8, with better accommodation or less time spent on the streets (Cox et al., 1998; Marshall et al., 1995; Korr & Joseph, 1996; Orwin et al., 1994; Shern et al., 2000; Shumway et al., 2008; Toro et al., 1997). However, no between‐group differences were found in long‐term reductions in homelessness in a variety of homeless populations (Burnam, 1995; Cox et al., 1998; Grace & Gill, 2014; Malte et al., 2017; Stahler et al., 1995; Toro et al., 1997). The findings on ICM interventions on mental health were mixed. In ICM groups we found modest reductions in psychiatric symptoms as well as psychological symptoms (deviant behaviour), youth self‐reports of depression problems, and total behavioural problems but not of antisocial behaviour (Cauce, 1994; Marshall et al., 1995; Toro et al., 1997). In contrast, other studies reported no notable between‐group differences in self‐esteem or mastery scores, youth's self‐reports on depression, antisocial behaviour on the Problem Behaviour Scale (PBS) or total behavioural problems (Clark & Rich, 2003; Felton et al., 1995; Marshall et al., 1995; Malte et al., 2017; Orwin et al., 1994; Shumway et al., 2008; Stahler et al., 1995). On the quality of life, ICM had a small effect with slight improvements in the quality of life and self‐esteem of homeless adolescents 13–21 years old, and satisfaction with living situations, finances as well as fewer life‐problems sub‐scores in ICM groups (Braucht 1995; Cauce 1994; Felton et al., 1995). Some studies reported no major changes in quality‐of‐life scores or better outcomes in the control group (Marshall et al., 1995; Shern et al., 2000). On substance use, ICM intervention had a small effect on substance‐ and drug‐use outcomes. Two studies found significantly (p < .05) lower composite scores for alcohol or recent alcohol and cocaine use across groups (Cox et al., 1998; Stahler et al., 1995); Other studies reported minimal improvements in problematic substance use or no significant between‐group differences in measures of alcohol or drug use (Burnam, 1995; Cauce, 1994; Malte et al., 2017; Orwin et al., 1994; Stahler et al., 1995; Toro et al., 1997). In three trials, ICM interventions resulted in reductions in hospitalisations and health‐care utilisation (Marshall et al., 1995; Rosenblum et al., 2002; Shumway et al., 2008). Overall ICM interventions showed no significant effects on participants staying employed (Braucht 1995; Cox et al., 1998; Orwin et al., 1994; Stahler et al., 1995). Regarding participants' income, some group effects favouring ICM groups using monthly public income assistance were found; however, there were no significant between‐group differences (Rosenblum et al., 2002; Toro et al., 1997).

Assertive community treatment

Overall, ACT interventions had a moderately positive effect on housing stability in homeless persons with mental illness who were treated with either continuous ACT or other ACT modalities—ACTO, IACT, NIACT (Clarke et al., 2000; Fletcher et al., 2008; Morse et al., 1997, 2006, 2008). Similarly, two trials found significant reductions in psychiatric symptoms or improved psychoticism subscales over time (Essock et al., 1998; Lehman et al., 1997). However, some studies that reported noticeable improvements in mental health did not find any group differences favouring using ACT interventions (Essock et al., 2006; Fletcher et al., 2008; Morse et al., 1997; Morse et al., 1997; Morse et al., 2006). On quality‐of‐life measures, the ACT intervention demonstrated some positive but not significant effects on general life satisfaction and QOL subscales, such as leisure and personal safety (Essock et al., 1998; Essock et al., 2006; Lehman et al., 1997). In the majority of the ACT trials, there were no significant improvements in alcohol consumption or substance use over time (Morse et al., 1992, 1997, 2006; Essock et al., 2006; Fletcher et al., 2008), except in one trial which found significant reductions in the alcohol‐, drug‐ and substance‐use and substance‐abuse scales in favour of ACT over SCM (Essock et al., 2006). Findings on alcohol or drug use were likely influenced by the use of varied tools of assessment as well as the rating scale used. Apparently, ACT interventions reduced days hospitalised or emergency‐department visits, among participants, compared to SCM interventions (Clarke et al., 2000; Essock et al., 1998; Essock et al., 2006; Lehman et al., 1997). Subsequently, ACT interventions had no significant impact on income compared to standard service or care (Morse et al., 1992, 1997). No evidence was found on the effects of ACT on employment outcomes in the selected trials.

Critical time intervention

Our systematic review yielded 5 studies on CTI. One study specifically explored family critical time intervention (FCTI) in a multidisciplinary community‐based service model targeted towards families and aiding in connecting them with social services and in forming supportive relationships with families and friends during critical times of transition from a shelter to community housing (Shinn et al., 2015).

Three of the four studies found that CTI significantly improved housing stability and reduced days spent homeless (Susser et al., 1997; Shinn et al., 2015) One study found a significant reduction in the amount of extended homelessness (more than 54 nights) specifically, with a relative risk of 0.53 (95% CI Taylor series, 0.27–1.01) (Susser et al., 1997). Within the trial that explored FCTI, families in the FCTI treatment group (in which the mother had a diagnosable mental illness or substance use problem) spent more time in community housing and had a lower average number of days until they moved into stable housing (91 compared to 199 days) (Shinn et al., 2015). One trial based out of the Netherlands did not find a significant difference in the number of days rehoused with CTI compared to TAU. The lack of significance of CTI vs TAU was thought to be partially explained by the very low rate of recurrent homelessness in both the CTI and care‐as‐usual treatment arms in this study (de Vet, 2017). The Netherlands' extensive social housing programme and increased intensity of follow up for those in usual care, compared to the United States, may have contributed to the low recurrent homelessness in both groups and the subsequent lack of significance of the type of intervention care (de Vet, 2017).

The results of CTI compared to TAU on mental health were mixed. Two studies found no significant difference in psychological distress, though in one study CTI had an added differential effect on psychological distress for participants experiencing less social support, suggesting that CTI may have more benefit in less‐supported individuals (de Vet, 2017). There was also no difference in mothers' mental health in the FCTI intervention compared to the TAU, though both the intervention and the control arms had significant improvements, over time, in mental‐health symptomatology. One study found that CTI appeared to significantly improve the symptoms of PTSD during follow up (adjusted MD, 7.27; 95% CI, −14.31 to −0.22, p = .04) Lako et al., 2018. Another trial demonstrated that CTI may also have a benefit for negative symptoms of schizophrenia (Herman et al., 2011). This finding was particularly intriguing, as negative symptoms of schizophrenia have a known disabling effect on patients' quality of life and are often extremely difficult to treat with medications (Correll & Schooler, 2020). Hierarchical regression analysis in this trial could not explain this improvement, by accounting for the reduction in homelessness. The authors proposed that CTI may provide “cognitive remediation”, encouraging participants to carry out executive tasks, which potentially re‐activated prefrontal cortical functions that were previously underutilized. Alternatively, the provision of social support and strengthening of relationships within times of critical transition may improve negative symptoms by improving feelings of hopelessness and loneliness (Herman et al., 2011). The findings of CTI benefits on particularly vulnerable subgroups—that is, participants with less social support, PTSD or schizophrenia—is important and requires further study.

Within children, one study found that FCTI appeared to reduce internalising behaviours and externalising barriers in children up to 5 years old (Shinn et al., 2015). For children between 6 and 10 years old, there were no effects of the intervention on mental health but both the CTI and usual‐care treatment groups had significant improvements over time, for mother‐reported internalising and externalising behaviours and child‐reported depressive symptoms. In adolescents aged 11–16 years, the FCTI group had a reduction in mother‐reported externalising behaviour, and this was not seen in the usual‐care group. At 24 months, the difference between these two groups was 6.2 (0.5 SD). Children's self‐report found no difference in externalising behaviours (Shinn et al., 2015). This trial suggests that FCTI has benefits beyond improving maternal symptomatology; further research is required to examine the effects of FCTI in children.

Two studies examined the effect of CTI on quality of life and found no between‐group differences during follow up (Lako et al., 2018; de Vet 2017). In one of these studies, however, the fidelity of results may have been impacted by the implementation of strengths‐based approaches in shelters just before the start of the study. Within this approach, a significant amount of post‐discharge services were also delivered to a majority of members in the control group, limiting the ability to detect between‐group outcome differences. (Lako et al., 2018). There was a trend towards reduced substance use in the CTI group, though it did not reach significance (De Vet 2017). Of note, however, in this study, baseline characteristics between the CTI versus the control group differed, with a significantly higher proportion of participants in the CTI group reporting excessive alcohol use in the past 30 days (21%), compared to the control group (20%) at baseline. Differences in baseline differences may have subsequently had an impact on the lack of significance of substance use outcome at follow up.

One study by Tomita (2012) found that participants receiving CTI had significantly reduced odds of psychiatric re‐hospitalisations during the final three observation intervals (OR = 0.11; 95% CI, 0.01–0.96). This impact was noted even after the completion of CTI intervention, and persisted even after controlling for housing stability. Reduced psychiatric re‐hospitalisation may be related to the impact of CTI on increasing social and community support and facilitating connection to external resources (Tomita 2012). In one study, FCTI participants (homeless mothers with high mental‐health needs) used more mental‐health services than the control group. These included mental‐health treatment in a hospital/clinic where the participant stayed overnight, services to help deal with a crisis, individual and/or group mental‐health counselling/therapy, services of a psychiatrist or other medical practitioner for the monitoring of psychiatric medications, and services of a case manager or some other person to help coordinate mental‐health services (Shinn et al., 2015; Susser et al., 1997). Another study examined mental‐health‐service utilisation (Susser et al., 1997) but provided only preliminary data; in this study, mental‐health utilisation was similar between the experimental groups but the CTI group used more services within each group than the control, particularly within outpatient clinics. These findings offer further support to the impact of CTI in connecting participants with mental health and community resources, during times of critical transition.

MAPs, SCFs and pharmacological interventions

This systematic review was intended to assess the effectiveness of SCFs, MAPs, pharmacological interventions for opioid use disorder and injectable antipsychotics for people who are homeless or vulnerably housed. No evidence from trials was identified; 20 articles were considered potentially relevant and were excluded. As SCFs begin to emerge, studies on such pilot projects are often observational due to ethical concerns, but often include a large proportion of homeless participants (Magwood, 2020). Existing reviews on SCFs primarily include observational studies (Kennedy et al., 2017; Potier et al., 2014). Studies of the effectiveness of MAPs have historically been conducted as case studies and small sample pilot projects that target individuals with severe alcohol dependence or who consume nonbeverage alcohol, as reported in one identified empty systematic review on MAPs (Muckle et al., 2012). Finally, the effectiveness of pharmacotherapeutic interventions is rarely assessed in transient and hard to reach populations. These results accurately reflect the existing evidence of MAPs, SCFs and pharmacotherapeutic interventions among homeless or vulnerably housed populations, as experimental evidence is often scarce in this transient population. To fill this gap, we have recently published an overview of reviews on this topic (Magwood, 2020).

Overall completeness and applicability of evidence

Permanent supportive housing

This systematic review presents evidence that PSH increases housing stability compared to usual care, promotes earlier exits from homelessness and fewer days spent homeless. Most study populations possessed a high degree of comorbid mental health and/or substance use, suggesting that PSH can be helpful even within high‐needs populations. The reproducibility of “Housing First” strategies across multiple cities demonstrates that this intervention has adaptability and relevance across multiple contexts.

Previously, access to housing was contingent on the attainment of abstinence and/or treatment and the stabilisation of underlying mental‐health disorders. Instead, our systematic review provides support for a “Housing First” strategy, advocating for the separation of housing and clinical services and the immediate provision of housing, with the aim of reducing homelessness, facilitating community integration and providing support and treatment with a recovery orientation (Aubry 2015). Long‐term data, up to 5.4 years, was examined in one single‐city site (Stergiopoulos et al., 2019); more research is required to further investigate the long‐term implications and effects of PSH.

Individuals who have a lived experience of homelessness are a diverse and heterogeneous population with different life courses and experiences that have shaped their vulnerabilities and resiliency (Aubry et al., 2012). For instance, individuals who become homeless at an older age tend to have less substance‐use and mental‐health comorbidities, compared to younger adolescents with a lived experience of homelessness (Aubry et al., 2016). Further research should focus on identifying specific populations and demographic groups within the overall group of persons with lived experiences of homelessness, who might benefit from targeted interventions, including improved success with PSH. Some subgroup analyses of gender and adolescent versus older participants were presented in this review, but this was sometimes under powered and hence primarily served as exploratory analyses. Mental health, quality of life, substance use, hospitalisations, income‐ and employment‐status outcomes would also benefit from further research within dedicated subgroup populations. Prior studies have shown some differences in outcomes between demographic groups. For instance, Tsemberis et al. (2004) found there were significant differences in rates of psychiatric‐symptom change over time, suggesting that decreases in symptomatology were more rapid for some individuals compared to others. A study within an ethnically diverse population in Toronto found differences in outcomes between racialized and nonracialized participants as well as foreign‐born vs Canadian‐born individuals (Stergiopoulos et al., 2015). Tsemberis et al. (2004) found that the HF programme was most successful in reducing hospitalisations for samples of people recruited from psychiatric hospitals, compared to those recruited from the street, who showed an overall low level of hospitalisations throughout the study period. Hence, research gaps that may be pursued in the future could include an examination of the differential magnitude of the effects of PSH based on age and gender, as well as among disabled persons and within minority groups.

Further study is also required to delineate improvements of PSH on quality of life, substance use, income and employment (as findings from existing studies are either limited or quite mixed). There is some limited evidence suggesting that PSH participants have improvements in their subjective condition that is specific to quality of life, compared to those receiving standard care. Only one study examined hybrid approaches to PSH (integrative vs continuum housing) (McHugo et al., 2004), though practical concerns of the actualisation of Housing‐First strategies may result in some policy‐makers favouring this strategy.

Income assistance

Income assistance interventions have been much less reviewed than other socioeconomic interventions due to the following challenges: (1) the complexity of income‐assistance interventions and the difficulty of isolating the specific effects from the impact of other socio‐demographic factors on populations with coexisting social and economic needs; (2) challenges in study design in terms of being able to assess the impacts on subjective outcomes (e.g., quality of life), which often requires significant follow up or funding to detect meaningful effect size; (3) individual outcome measurements can be affected by political‐economic dynamics and systemic barriers within a designed study period (Shahidi et al., 2019). Recently Aubry et al. (2020) appraised the evidence on the effect of income‐assistance interventions on the social and health outcomes and reported the promising positive effect of housing subsidies with case management on housing stability. However, evidence on the effects of income‐assistance interventions for the homeless populations remains inconclusive and lacking realist review on the long‐term effects and the interaction with other social service components for the homeless population (Pawson et al., 2005). Our current review assessed the effect of income‐assistance interventions in the context of health and social outcomes and provided an up‐to‐date summary of a growing body of primary research on the effect of income‐assistance interventions over the past decades. Inconsistent findings were reported on those programmes that were associated with income‐assistance interventions that ranged from rental assistance in the form of housing subsidies (Gubits et al., 2018; Hurlburt et al., 1996; Pankratz et al., 2017; Rosenheck et al., 2003; Wolitski, 2009), IPS (Ferguson, 2018; Poremski et al., 2015), housing assistance with income support (Forchuk et al., 2008), financial education (Booshehri 2017), to CWT (Kashner, 2002). The diversity of the intervention characteristics, participant profiles, and outcome measurements contributed to the inconsistency of the effectiveness. There was a lack of standardised controls or comparisons across the eligible studies. Extra caution is required when interpreting the results for future implications.

SCM and peer support interventions

Standard case management

The nature of the case‐management interventions in this review varied in the intensity of the programme and study population, with the majority of the trials conducted in the United States. Previously, evidence on the SCM model was associated with short‐term outcomes but limited effects regarding treatment retention, employment, and housing stability in individuals with both mental illness and substance use disorders. Our review findings were similar, with little or no significant long‐term benefit across the study outcomes such as housing stability, mental health, and substance use. In contrast, a study reported improvements in housing stability, reduced substance use and employment barriers in homeless substance users, evidence in our study supported only a short‐term positive effect on housing stability (Magwood et al., 2019). In one trial, SCM was associated with elevated levels of hostility and depression in a homeless female population (Nyamathi et al., 2001).

Peer support

Our systematic review examined six studies that provided mixed evidence on the effectiveness of peer support interventions among individuals with lived experience of homelessness. This inconsistency could, very well, be attributed to the heterogeneity in the design and implementation of peer support programmes. Two studies used peer coaches to provide support to homeless individuals in the context of receiving temporary housing (Ellison et al., 2020; Lapham et al., 1996), and even though we were able to isolate the effect of this peer support component from the housing programme, we were not able to determine whether the conjugation of temporary housing to peer support may have put study participants in an advantage to benefit from this intervention. In another two studies (Corrigan et al., 2017; Nyamathi et al., 2001), peer supporters were recruited to reflect participants' ethnic background, but this ethnic matching did not seem to promote added benefit among individuals with lived experience of homelessness. Across all studies, assigning participants to peer support programmes was not conclusively associated with housing, mental health, or social improvements relative to usual care, which suggests that peer support cannot serve as a stand‐alone intervention to promote stability in these outcomes. More research, however, is needed to explore whether coupling peer support with more permanent housing programmes could improve housing and health.

Mental health interventions

Our systematic review examined mental health interventions that supported people with mental illness and substance use disorders who were also in homeless populations and was similar to a recent review by Ponka et al. (2020) and an earlier review by De Vet (2013). To our knowledge, this systematic review offers a comprehensive evaluation of effectiveness and outcomes of interventions including ICM, ACT and CTI; and incorporated wider definitions for specific interventions and studies from other high‐income countries and regions reporting evidence on case management in homeless populations as global public health problems. In addition, Aubry (2020) found evidence that case management intervention can have significant benefits when provided in conjunction with PSH (Aubry et al., 2020). Our review findings agree with reports of the increased rate of initiation, engagement retention, reduced hospital visits, and better treatment outcome with twice as many clients with substance use problems treated with ICM, although client's hospital stays remained same with TAU groups (Morgenstern et al., 2006; Kuerbis, 2011/03; Stergiopoulos et al., 2015). However, only ICM was found to consistently improve income outcomes, with significant improvements in access to financial assistance and reductions in unmet financial needs.

Our study supports strong evidence on the effectiveness of ACT in homeless clients with both mental health and substance use disorders and demonstrates substantial benefits with better outcomes such as housing stability, quality of life as well as lesser hospital stays and emergency visits. ACT interventions were cost‐effective offering both crisis intervention and psychosocial interventions for persons with complex needs such as persons with severe mental illness or dual disorders and homeless. Hence, there are cost benefits when the overall health‐care systems and society are considered, however, some researchers find the approach somewhat authoritarian, forced and inconsistent with recovery‐oriented mental health practice (Tsai et al., 2011). Furthermore, CTI appears to reduce homelessness and increase days spent in stable housing, with three out of four studies showing improvements in housing stability (de Vet, 2017). Also, CTI may have a differential benefit in reducing symptoms of PTSD and negative symptoms of schizophrenia, though more research should be done to confirm these findings. The effectiveness of family critical time intervention (FCTI) showed some promising effects on the impact of homelessness, with mixed effects on reducing internalising/externalising behaviours in children in a single study. While we identified positive impacts in housing stability in the homeless population using interventions with greater intensity like ICM, ACT and CTI, our review found insufficiency studies on the effects of ACT and CTI on income and employment outcomes. Also, the heterogeneity of these complex interventions, participant profiles, coupled with the inexactness in the mechanisms and key features that promote effectiveness varies which presents a challenge in the assessment of outcomes as well as contributes to the variance in effectiveness. Regardless, the effectiveness of strength‐based case‐management and mental health interventions appears to be related to both the intensity of the models and the fidelity of the programmes to comprehensively address the needs of homeless populations, particularly those with severe mental health conditions or who are experiencing transitions in care (Dieterich, 2017). Again, the more intensive models of case management (ICM or ACT) and with lower caseloads and potential longer engagement with case‐managers provide services that extend beyond care coordination and outreaches, therefore have a greater chance and effects in improving causal social determinants of health that maintain the cycle of homelessness (De Vet, 2013; Ponka et al., 2020). Another critical factor is the role of caseworkers as advocates for clients' access to income benefits and locating housing options leads to improvements in housing stability (Sosin et al., 1995). Also, of particular interest, is the role of trust in the case‐manager‐client relationship as well the continuity of care being an integral element in the efficacy of case‐management programmes (Magwood et al., 2019). Other capable variants of the programmes with unique and novel case‐manager roles that include peer‐led initiatives and people with lived experience appear promising in addressing the cycle of homelessness in populations, but these needs further evaluation (Tsai et al., 2011; Greene et al., 2015; Gagne et al., 2018). Our findings suggest that case management and mental health interventions need to be continuous, community‐based and intensive to maintain and increase the gains achieved. These findings are in agreement with other previously published reviews, such as Mueser (1998), Coldwell & Bender (2007), Hwang (2005); and Vanderplasschen et al., (2007), respectively.

Quality of the evidence

Risk of bias in included studies provides a detailed description, and summary, of primary study bias judgements. Furthermore, these risk of bias assessments were considered as part of the GRADE assessment of the certainty of evidence. We assessed the certainty of evidence for housing stability outcomes across all interventions. Overall, the certainty of evidence for interventions aimed at reducing homelessness ranged from very low to moderate. For PSH, there is moderate certainty evidence that PSH increases housing stability (summary of findings Table 1). This evidence comes from two randomised trials with concerns regarding selection, performance and detection biases. Low certainty evidence on income assistance interventions reduced episodes of homelessness and increased number of days stably housed (summary of findings Table 2). Certainty of evidence pertaining to SCM (summary of findings Table 3), ICM (summary of findings Table 4) and CTIs (summary of findings Table 6) were also deemed low. Finally, the evidence on housing stability outcomes from ACT (summary of findings Table 5) and peer support interventions (summary of findings Table 7) ranged from low to very low certainty, often due to single studies with small sample sizes (<300 participants) and few events (<100 observations).

Overall, for PSH interventions, there is moderate confidence in the estimated effect of housing stability, the true effect is likely to be close to the estimated effect, but there is a possibility that it is substantially different. For all other interventions (income, SCM, ICM, ACT, and peer support) there is very little to limited confidence in the estimated effect, the true effect is likely to be substantially different from the estimated effect reported in this review.

Potential biases in the review process

Our review provides a comprehensive and robust analysis on the effectiveness of several community‐based interventions targeting individuals with lived experience of homelessness. This work, however, is not without certain inherent contextual and methodological limitations that challenged our efforts to draw generalisable and certain conclusions from our findings. First, the differences in how interventions were conceptualised and implemented in pragmatic conditions while falling under the same definition introduced a degree of clinical heterogeneity that prevented us from undertaking a more inclusive pooling of effect estimates, and therefore we resorted to narratively synthesising the majority of findings for this review. This, as well, was true for how usual care or “treatment as usual” conditions were defined and implemented, which affected the magnitude of effect estimates within a certain comparison of outcomes based on the intensity of usual care services relative to the intervention of interest. Second, the between‐study heterogeneity in the characteristics and levels of need of target populations has precluded us from generalising our findings to a wider population of individuals with lived experience of homelessness, as the majority of study participants had suffered from long term mental health or problematic substance use conditions prior to their enrolment into the study. This was apparent in our GRADE certainty of evidence assessments as most of the findings were of low to moderate certainty, indicating that prospective studies with a larger sample size that encompasses individuals with low levels of mental health or substance use needs will likely change the magnitude of effect estimates and certainty of evidence. Thirdly, the majority of studies took place in North American countries (i.e., The United States and Canada) and thus, the interpretation of effectiveness and cost‐effectiveness findings should be taken with caution in high income countries with contextual and global differences in health care and social welfare systems. Policy making strategies and decisions to implement a certain intervention should take these contextual differences into consideration. Finally, in our attempt to curate the most accurate evidence, we restricted our inclusion criteria to experimental controlled trials with quantitative outcome measurements. This condition may have provided higher internal validity to our findings and precision to our effect estimates, but it has also excluded findings from observational and qualitative studies which, in turn, could affect the external validity of our results.

Agreements and disagreements with other studies or reviews

Permanent supportive housing

To our knowledge, our systematic review is the most up‐to‐date and comprehensive review available, examining a wide range of outcomes including housing stability, mental health, quality of life, substance use, hospitalisations, income and employment, as well as presenting practical cost‐effectiveness data for each intervention.

Our review presents results that are consistent with prior published research. A prior Campbell review (Munthe‐Kaas et al., 2018), published in February 2018, also reported an improvement in housing stability with nonabstinent contingent housing. Unlike our review, this publication included only RCTs and restricted inclusion to studies which had followed patients for at least a year. All RCTs included in this review had a high risk of bias, particularly due to poor randomisation or poor allocation concealment procedures, performance bias, detection bias, attrition bias or reporting bias (Munthe‐Kaas et al., 2018). Though RCTs are touted to be a gold‐standard means of evaluating the effectiveness of an intervention, the significant vulnerability of the homeless population may result in ethical dilemmas in withholding services, leading to some investigators pursuing alternative study designs. Therefore, to ensure that our findings are based on comprehensive evidence compatible with the pragmatism of housing interventions and transient nature of individuals with lived experience of homelessness, we elicited effectiveness data from a more broad range of clinical trials. Other more recently published reviews, Baxter et al. (2019) and Aubry et al. (2020) also found benefits in PSH strategies. Similar to our review, Baxter et al. (2019) demonstrated that intervention participants spent more days housed, were more likely to be housed at 18‐24 months, and had fewer emergency‐department visits and hospitalisations. Of note however, Baxter et al. (2019) examined only four RCTs, in order to enable a meta‐analysis synthesis of the data, and chose to encompass rental incentives and vouchers in their definition of PSH. Replication of findings with a higher quantity and broader range of publications provides further evidence of the validity and reproducibility of the intervention. Peng et al. (2020) found that HF programmes reduced homelessness by 88% when compared with Treatment First programmes, and 89% compared to TAU. Similar to our review, HF programmes did not significantly change mental health and substance use as compared with TAU, but was associated with less emergency department use and hospitalisations. Unlike our study, HF programmes were also found to improve clients' quality of life score, where‐as our review demonstrated mixed findings (Peng et al., 2020). Mixed data most likely reflects subjectivity and difficulty in measurement and quantification of quality of life. Further research is needed to explore the effect of HF interventions on quality of life. It is noteworthy to mention that Peng et al. (2020) did not seek to assess the certainty of evidence derived from their data and chose to exclude studies that did not meet a certain quality threshold set by the authors.

In contrast, Bassuk et al. 2014 did not find an effect of community affordable housing on residential stability. However, this review had significant limitations. Only six studies were identified and all except two were deemed to be methodologically “weak”. Most explored only baseline and follow‐up data without a control or comparison group, and were deemed by authors to have poor reporting quality. All six studies came from “grey literature” and mostly consisted of government and foundation commission studies (Bassuk et al. 2014).

Our review incorporates new research including 6‐year longitudinal‐outcome data and offers perspectives on a wider range of important psychological and social outcomes. Unlike many prior reviews, our synthesis also provides cost‐effectiveness data, which is an integral component to inform policy and decision‐making processes. Uniquely, our review incorporated into review processes persons with lived experience of homelessness, so as to promote engagement, health equity and community‐trust relations. Agreements with the vast majority of prior reviews offer policy‐makers a more robust evidence base to guide their decision making.

Income assistance

Based on our latest literature review, the effect of income‐assistance interventions on health and social conditions for persons experiencing homelessness had not been systematically reviewed in the context of comprehensive social interventions prioritised for the homeless population. Aubry et al. (2020) reviewed the isolated effects of income‐assistance interventions for people experiencing homelessness and reported promising results in consistence with our findings. The studies which investigated the income supplement for low‐income families and pregnant women have also demonstrated positive outcomes on health‐related outcomes and healthcare utilisation along with the importance of longitudinal support, patient advocacy, and comprehensive services (Brownell et al., 2016; Forget, 2011).

SCM and peer support interventions

This systematic review offers a comprehensive evaluation of the effectiveness and outcomes of SCM interventions. Two previous systematic reviews (De Vet 2013; Ponka et al., 2020) reported similar mixed results that suggest SCM might carry the potential to improve housing outcomes. however, to the best of our knowledge, no systematic review or meta‐analysis has examined the isolated effect of peer support interventions among individuals with lived experience of homelessness. One systematic review (Munthe‐Kaas et al., 2018) examined the effectiveness of peer support as an adjacent component to a more ICM programme and found no significant benefit in housing stability associated with that programme relative to usual care of less ICM.

Mental health interventions

This systematic review offers a comprehensive evaluation of the effectiveness and outcomes of mental‐health interventions, including ICM, ACT and CTI. It incorporated more extensive definitions for specific responses and studies from other high‐income countries and regions, reporting evidence on managing mental health in homeless populations as a global public health problem. A recent systematic review (Ponka et al., 2020), and an earlier report (De Vet 2013), reported similar results on the effectiveness of mental health interventions that supported people with mental illness and substance as in this review. Our review confirmed significant positive findings on housing outcomes, particularly for ICM and ACT and, to a lesser degree CTI in improving housing access and stability. However, variations in the sub‐context of social and health determinants exist.

Morandi et al. (2017) and Stergiopoulos (2015a) reported reductions in psychiatric emergency visits, substance use levels, quality of life, social functioning, and engagements where ICM is integrated into other strength‐based approaches for at‐risk populations. Also, our findings are congruent with a meta‐analysis on ACT interventions, which reported more substantial benefits over SCM models in reducing the odds of homelessness and severity of symptoms in homeless persons with severe mental illness (Coldwell & Bender, 2007; Mueser, 1998; Vanderplasschen et al., 2007). Our findings on the benefits of ACT interventions agrees with the conclusions of a reductive effect on rates of relapse amongst youth undergoing opioid rehabilitation (Fishman et al., 2020). For CTI, our results were relatively consistent with an earlier review (De Vet, 2013), except for new evidence indicating that CTI decreased psychiatric symptoms. Another recent RCT reported the feasibility of CTI with mental health, employment or education, and better housing stability favouring a housing outreach programme—collaboration (HOP‐C) (Kidd et al., 2020). Nevertheless, there is still limited evidence, particularly in assessing the impact of mental health interventions (ACT and CTI) on income and employment outcomes in selected trials. In general, Ponka et al. (2020) highlighted the context of the intervention, notably where the intensity and role of case managers in the Netherlands differed in comparison to those in the United States or North America. Hence, our review highlights the potential impact of high fidelity and intensity of the intervention. ICM interventions are crucial in comprehensively addressing the needs of homeless or vulnerably housed persons. Our findings suggest adherence to this model of case management, which is continuous, community‐based and intensive, would maintain or increase the gains achieved.

AUTHORS' CONCLUSIONS

Implications for practice

Our review suggests that PSH programmes improve long‐term housing stability for up to 5.4 years compared to usual services. Income assistance, and high intensity case management interventions may also improve housing stability compared to usual services. The intensity and fidelity of the PSH and case management interventions strengthen the results. However, the interventions have mixed results for mental health, quality of life, substance use, hospitalisations, income and employment outcomes. The quality of the evidence varied from very low to moderate. The risk of bias including poor reporting, lack of blinding, and allocation bias reduced the certainty of the results. Given that most studies included individuals who had transitioned to living with chronic homelessness and often had a high burden of severe mental illness, it is possible that the overall impact of housing‐related interventions is in fact underestimated.

Preventing homelessness and providing early housing interventions has major practice and policy implications, particularly in 2021–2022 as the COVID‐19 pandemic disrupts economies, displaces populations, and threatens people already living with homelessness. Policymakers must reckon with a possible epidemic of complex social and public health challenges that may arise as more people transition to chronic homelessness. This review provides solid evidence on the value of PSH interventions and also suggests benefit of income and case management strategies. Policymakers will need imagination and innovation to scale up these interventions, including increasing their intensity and fidelity when appropriate. The absence of review evidence on substance‐use interventions for people living with homelessness represents an important research and policy gap.

This review has informed the development and publication of a clinical practice guideline, geared at preventing homelessness and improving the social and health outcomes of homeless and vulnerably housed individuals. The novel guideline outlines evidence‐based approaches and recommendations for initial priority steps. It seeks to reframe practice approaches in caring for patients with lived experience of homelessness, emphasising effective upstream interventions and promoting increased collaboration in the delivery of care (Pottie et al., 2020).

Indeed, preventing homelessness with responsive housing programmes has major cost and policy implications. Further inter‐sectoral collaboration will be required by health care providers, community health organisations, public health officials and policy makers to facilitate increased coordination of services, improve accessibility and address resource fragmentation. Evidence‐based reviews like this one can guide practice and outcome research and contribute to advancing international perspectives on the effectiveness of interventions to prevent and end homelessness.

Implications for research

PSH interventions have emerged as effective core elements in the care of homeless and vulnerably housed populations. However, there is still a need for more pragmatic research to understand inconsistent and mixed results on mental health, quality of life, substance use, hospitalisations, income and employment outcomes. As well, there are also ongoing gaps that warrant more research, including exploring peer support programmes, SCFs and other community substance use programmes for homeless populations. Further research should also study the intersectional and differential effect of certain interventions on specific populations, including Indigenous and migrant groups, recognising the heterogeneity of the homelessness population. Factors such as age, demographics, social identities, comorbidities and pathways into homelessness are all important considerations in identifying the benefit and harm of interventions. Health equity research may offer useful interdisciplinary methods and approaches to improve outcomes for sub‐groups within the overall population of persons with homelessness.

There is also a role for expanding implementation research for community interventions. Studies report significant resource and logistical barriers implementing programmes to meet the complex social and health needs of this vulnerable population. Persons with lived experience of chronic homelessness may harbour considerable retrospective bias, earned from years of experience in and out of housing shelters, which may deter trust and slow the implementation of new interventions. Research will be needed to help guide practice, public health and policy makers in actualisation of evidence‐based recommendations. Our review did not seek to understand the mechanisms behind why certain services may hold benefit over others. By improving mechanistic knowledge, future realist reviews may be able to guide the development of multisectoral and targeted interventions to better affect downstream consequences of homelessness with respect to mental health, quality of life, morbidity and mortality.

CONTRIBUTIONS OF AUTHORS

Content: Aliza Moledina (Permanent Supportive Housing and Critical Time Intervention); Jui‐Hsia Hung (Income‐Assistance Intervention); Ammar Saad (Peer Support), Eric Agbata (Standard Case Management, Intensive Case Management, Assertive Community Treatment), Olivia Magwood (Supervised consumption facilities, Managed alcohol programmes, opioid agonist therapy), Kednapa Thavorn (Cost‐effectiveness)Systematic review methods: Ammar Saad, Olivia Magwood, Kevin PottieStatistical analysis: Ammar SaadInformation retrieval: Ammar Saad, Olivia Magwood

DECLARATIONS OF INTEREST

None declared

PRELIMINARY TIMEFRAME

August 25, 2020

(Approximate date for submission of the systematic review.)

PLANS FOR UPDATING THIS REVIEW

We will update our search prior to submitting this review for publication to ensure that our findings are up‐to‐date. As well, the reviews will be updated using the PICO question in 4 years. Kevin Pottie will be responsible for updates.

DIFFERENCES BETWEEN PROTOCOL AND REVIEW

Following the publication of our protocol (Pottie et al., 2019), we engaged key stakeholder groups, such as individuals with lived experience of homelessness, in the review development process. We conducted consultations with these stakeholders as well as experts in the field of homeless health and health equity, and decided to prioritise housing stability as a primary outcome of our review to better highlight the effectiveness of permanent supportive housing on its primary intended purpose of mitigating homelessness in its conceptual definition; increasing housing stability and decreasing days on the street or in shelters. Other health and social outcomes such as mental health, quality of life, substance use, hospitalisation and health care utilisation, employment, and income were considered to be secondary outcomes of this review. As such, our assessment of evidence certainty using the GRADE methodology (Please see Methods) was exclusive to the primary outcome of interest as our primary conclusions from this review pertain to housing stability.

PUBLISHED NOTES

Characteristics of studies

Characteristics of included studies

Aubry et al. (2016)

Risk of bias table

Booshehri (2017)

Risk of bias table

Braucht (1995)

Risk of bias table

Burnam (1995)

Risk of bias table

Cauce (1994)

Risk of bias table

Chalmers 2010

Risk of bias table

Cherner et al., 2017

Risk of bias table

Clark et al., 1998

Risk of bias table

Clarke et al., 2000

Risk of bias table

Clark & Rich, 2003

Risk of bias table

Conrad et al., 1998

Risk of bias table

Corrigan et al., 2017

Risk of bias table

Cox et al., 1998

Risk of bias table

Culhane et al., 2002

Risk of bias table

De Vet 2017

Risk of bias table

Dickey et al., 1997

Risk of bias table

Ellison et al., 2020

Risk of bias table

Essock et al., 1998

Risk of bias table

Essock et al., 2006

Risk of bias table

Evans et al., 2016

Risk of bias table

Felton et al., 1995

Risk of bias table

Ferguson, 2018

Risk of bias table

Fletcher et al., 2008

Risk of bias table

Forchuk et al., 2008

Risk of bias table

Gilmer et al., 2009

Risk of bias table

Gilmer et al., 2010

Risk of bias table

Goldfinger et al., 1999

Risk of bias table

Grace & Gill, 2014

Risk of bias table

Graham‐Jones et al., 2004

Risk of bias table

Gubits et al., 2018

Risk of bias table

Gulcur 2003

Risk of bias table

Herman et al., 2011

Risk of bias table

Holtgrave et al., 2013

Risk of bias table

Hunter et al., 2017

Risk of bias table

Hurlburt et al., 1996

Risk of bias table

Hwang et al., 2011

Risk of bias table

Kashner, 2002

Risk of bias table

Korr & Joseph, 1996

Risk of bias table

Lako et al., 2018

Risk of bias table

Lapham et al., 1996

Risk of bias table

Larimer, 2009

Risk of bias table

Latimer et al., 2019

Risk of bias table

Lehman 1997

Risk of bias table

Lehman 1999

Risk of bias table

Lenz‐Rashid, 2017

Risk of bias table

Lim et al., 2018

Risk of bias table

Lipton et al., 1988

Risk of bias table

Malte et al., 2017

Risk of bias table

Mares & Rosenheck, 2011

Risk of bias table

Marshall et al., 1995

Risk of bias table

Martinez & Burt, 2006

Risk of bias table

McHugo et al., 2004

Risk of bias table

Morse et al., 1992

Risk of bias table

Morse et al., 1997

Risk of bias table

Morse et al., 2006

Risk of bias table

Nyamathi et al., 2001

Risk of bias table

Nyamathi et al., 2016

Risk of bias table

Okin et al., 2000

Risk of bias table

Orwin et al., 1994

Risk of bias table

Pankratz et al., 2017

Risk of bias table

Pauley et al., 2016

Risk of bias table

Poremski et al., 2015

Risk of bias table

Rich & Clark, 2005

Risk of bias table

Rosenblum et al., 2002

Risk of bias table

Rosenheck et al., 2003

Risk of bias table

Sadowski et al., 2009

Risk of bias table

Schinka et al., 1998

Risk of bias table

Shern et al., 2000

Risk of bias table

Shinn et al., 2015

Risk of bias table

Shumway et al., 2008

Risk of bias table

Siegel et al., 2006

Risk of bias table

Sosin et al., 1995

Risk of bias table

Srebnik et al., 2013

Risk of bias table

Stahler et al., 1995

Risk of bias table

Stefancic & Tsemberis, 2007

Risk of bias table

Stergiopoulos et al., 2015

Risk of bias table

Stergiopoulos et al., 2019

Risk of bias table

Susser et al., 1997

Risk of bias table

Toro et al., 1997

Risk of bias table

Towe et al., 2019

Risk of bias table

Tsemberis et al., 2004

Risk of bias table

Upshur et al., 2015

Risk of bias table

Weinreb et al., 2016

Risk of bias table

Wolff, 1997

Risk of bias table

Wolitski 2009

Risk of bias table

Yoon et al., 2017

Risk of bias table

Young et al., 2009

Risk of bias table

Characteristics of excluded studies

Summary of findings tables

Additional tables

Data and analyses

1.Housing stability

Sources of support

Internal sources

Stakeholders, Canada

Community scholars and other persons with lived experience provided assistance in priority setting for the review.

External sources

Inner City Health Associates, Canada

Financial Support

Feedback

Acknowledgements

ACKNOWLEDGEMENTSThe authors would like to thank Doug Salzwedel for his systematic search services and expertise, Glenna Jenkins for her editorial input, Joseph Benjamen for assistance with database management, and all working group members of the Homeless Health Research Network who contributed towards screening, selection, data extraction and critical appraisal.

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288. Protocol NCT00057161.* Homelessness prevention: Psychiatric care with representative payeeship. U.S. National Library of Medicine ClinicalTrials.gov (Protocol Registration number: nct00057161) https://www.clinicaltrials.gov/ct2/show/NCT00057161
289. Protocol NCT00490581. Evaluation of housing first initiative for Chicago homeless with chronic medical illness. U.S. National Library of Medicine ClinicalTrials.gov (Trial Registration number NCT00490581) https://clinicaltrials.gov/show/NCT00490581
290. Protocol NCT00621465. Critical time intervention in the transition from hospital to community in people with severe mental illness. U.S. National Library of Medicine ClinicalTrials.gov (Protocol Registration number: nct00621465) https://clinicaltrials.gov/ct2/show/NCT00621465
291. Protocol NCT01346514. Addiction housing case management for homeless veterans (AHCM). U.S. National Library of Medicine ClinicalTrials.gov (Trial registration number: NCT01346514) https://clinicaltrials.gov/show/NCT01346514
292. Protocol NCT01430741. MISSION‐Vet HUD‐VASH implementation study. U.S. National Library of Medicine ClinicalTrials.gov (Trial registration number NCT01430741) https://clinicaltrials.gov/show/NCT01430741
293. Protocol NCT01550757. Aligning Resources to Care for Homeless Veterans (ARCH). U.S. National Library of Medicine ClinicalTrials.gov (Protocol Registration Number: nct01550757) https://clinicaltrials.gov/ct2/show/NCT01550757
294. Protocol NCT01570712. Evaluation of the "Housing First Program" in Homeless Patients With Severe Mental Disorders in France. U.S. National Library of Medicine ClinicalTrials.gov (Trial registration number NCT01570712) https://clinicaltrials.gov/show/NCT01570712
295. Protocol NCT01932801. Harm Reduction With Pharmacotherapy (HaRP). U.S. National Library of Medicine ClinicalTrials.gov (Trial registration number NCT01932801) https://clinicaltrials.gov/show/NCT01932801
296. Protocol NCT02258425. Homeless Female Offenders Returning to the Community. U.S. National Library of Medicine ClinicalTrials.gov (Trial registration number NCT02258425) https://clinicaltrials.gov/show/NCT02258425
297. Protocol NCT02440360. Pay For Success: Permanent Supportive Housing for the Chronically Homeless. U.S. National Library of Medicine ClinicalTrials.gov (Protocol Registration number: nct02440360) https://clinicaltrials.gov/ct2/show/NCT02440360
298. Protocol NCT02553616. An Intervention to Promote Healthy Behaviors in Homeless Youth. U.S. National Library of Medicine ClinicalTrials.gov (Protocol Registration Number: nct02553616) https://clinicaltrials.gov/ct2/show/NCT02553616
299. Protocol NCT02723058. The Integrated Care Model for Homeless Mothers. U.S. National Library of Medicine ClinicalTrials.gov (Protocol Registration number: nct02723058) https://clinicaltrials.gov/ct2/show/NCT02723058
300. Protocol NCT02816294. Housing Prescriptions as Health Care. U.S. National Library of Medicine ClinicalTrials.gov (Protocol Registration number: nct02816294) https://clinicaltrials.gov/ct2/show/NCT02816294
301. Protocol NCT03334825. Enhanced Housing Placement Assistance (EHPA). U.S. National Library of Medicine ClinicalTrials.gov (Protocol Registration number: nct03334825) https://clinicaltrials.gov/ct2/show/NCT03334825
302. Protocol NCT03766165. Microenterprise intervention to reduce sexual risk behaviors in young adults (EMERGE). U.S. National Library of Medicine ClinicalTrials.gov (Protocol Registration number: nct03766165) https://clinicaltrials.gov/ct2/show/NCT03766165
303. Protocol NCT03770221. Coordinating access to care for people experiencing homelessness (CATCH‐FI). U.S. National Library of Medicine ClinicalTrials.gov (Trial registration number NCT03770221) https://clinicaltrials.gov/show/NCT03770221
304. *Protocol NCT03779204. Effect of a rent subsidy and mentoring on youth transitioning out of homelessness. U.S. National Library of Medicine ClinicalTrials.gov (Trial registration number NCT03779204) https://clinicaltrials.gov/ct2/show/NCT03779204
305. Protocol NCT03910218. Come as you are—Assessing the efficacy of a nurse case management HIV prevention and care intervention among homeless youth. U.S. National Library of Medicine ClinicalTrials.gov (Protocol Registration number: nct03910218) https://clinicaltrials.gov/ct2/show/NCT03910218
306. Protocol NCT04012697. Peer support for homelessness in the emergency department. U.S. National Library of Medicine ClinicalTrials.gov (Trial registration number NCT04012697) https://clinicaltrials.gov/show/NCT04012697
307. Protocol NCT04135703. Prevention of OUD: the HOME Project (Housing, Opportunities, Motivation and Engagement). U.S. National Library of Medicine ClinicalTrials.gov (Trial registration number NCT04135703) https://clinicaltrials.gov/show/NCT04135703
308. Protocol NTR1640. Care for each other. Stimulating Fellow Care in sheltered housing for homeless people. Netherlands Trial Register (Protocol Registration number: NTR1640) https://www.trialregister.nl/trial/1562
309. Protocol NTR3254. A strengths based method for homeless youths: effectiveness and fidelity of Houvast. Netherlands Trial Register (Protocol Registration number: NTR3254) https://www.trialregister.nl/trial/3106
310. Protocol NTR3463. EffectIve: Study of the effectiveness of Critical Time Intervention after residence in Dutch women's shelters. Netherlands Trial Register (Protocol Registration number: NTR3463) https://www.trialregister.nl/trial/3316
311. Protocol NTR896. Assertive community treatment (ACT) versus case management in treating homeless patients with severe mental illness; a randomized controlled trial. Netherlands Trial Register (Protocol Registration number: NTR896) https://www.trialregister.nl/trial/881
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