	Introduction

For more than a decade, Congress and the federal government have focused on ending homelessness among the chronically homeless population, a group characterized by extended periods of time spent living on the street or other places not meant for human habitation and having one or more disabling conditions. In addition, it summarizes the research regarding chronically homeless individuals who move into PSH (" Research on Permanent Supportive Housing for Chronically Homeless Individuals "). Federal Definition of Chronic Homelessness

The federal definition of chronic homelessness grew out of the George W. Bush Administration's plan to end chronic homelessness and an interagency project, the Collaborative Initiative to Help End Chronic Homelessness, that was funded in 2003. The best data in recent years comes from annual community point-in-time counts of people experiencing homelessness. Homeless individuals with mental illness and substance use disorders may struggle to earn income and otherwise stabilize their lives in order to achieve and maintain housing without assistance. Most simply, permanent supportive housing (PSH) is housing that is not time-limited and where services are available for residents. Housing First makes many services available but does not require residents to use them, nor does it require abstinence or medication compliance. The Housing First model was pioneered by the New York provider Pathways to Housing. It also stresses the importance of resident choice about where to live and the type and intensity of services, with services structured to fit individual resident needs. These included (1) a collaboration among HUD, HHS, and VA (the Collaborative Initiative to Help End Chronic Homelessness ) that funded housing and treatment for chronically homeless individuals; (2) a HUD and DOL project called Ending Chronic Homelessness through Employment and Housing , through which HUD funded permanent supportive housing and DOL offered employment assistance; and (3) a HUD pilot program called Housing for People Who Are Homeless and Addicted to Alcohol that provided supportive housing for chronically homeless persons. The HUD Homeless Assistance Grants are the primary way the federal government funds housing for people experiencing homelessness. (The target has since been updated to 2017. ) There are five common outcomes that appeared most frequently in the research: 
Housing status and stability —Typically measured by the number of days housed or days spent homeless after moving into housing; P ublic service use and costs —Evidenced by the number of visits to service providers or the amount of public funds spent on services such as hospitalizations, counseling, or shelter before and after a housing intervention; Substance use —Measured based on whether days drinking or using drugs increase or decrease after moving into housing; Mental health —Evaluated by such factors as psychiatric symptoms or time spent in treatment or psychiatric hospitals; Resident satisfaction and quality of life —Evaluated based on residents' impressions of housing and other aspects of their lives based on residents' responses to survey questions after moving into housing. A successful outcome in one area—such as stable housing—may not necessarily translate to a successful outcome in other areas, such as improved mental health or less use of alcohol and drugs. The results from these studies support the Housing First principle that individuals need not be housing-ready to succeed in ending a long-term spell of homelessness. Public Service Use and Costs

An impetus for prioritizing permanent supportive housing for chronically homeless individuals is the idea that housing can reduce the use of expensive services, often paid with public funds, such as hospitals and emergency rooms; law enforcement resources, jails, and prisons; and temporary emergency shelter. Some descriptions of PSH, particularly those in the media, indicate that cost reductions from PSH should be expected. However, unlike housing stability, where providing PSH largely improved this outcome, findings regarding cost reductions are somewhat mixed. Factors accounting for the differences in service use and cost from one study to another include the neediness of the population receiving housing (very high-need populations with co-occurring mental illness and serious addictions likely have more opportunities to reduce service use); the type of assistance received by comparison groups, if any (a comparison group in transitional housing may have fewer differences in service use than one receiving no housing assistance); the number of costs included by researchers (if only a limited number of costs are assessed, or if the costs of housing are not included, it may not give a full picture of a housing intervention); and the length of the follow-up period (changes may be more positive in a short amount of time after receiving housing or could take longer to occur). Among veterans enrolled in the HUD-VASH program (which prioritizes chronically homeless veterans) in FY2010, 42% had a serious mental illness. While the evidence shows that PSH can be a solution to chronic homelessness, it is less clear whether PSH will "solve" other issues faced by homeless individuals or reduce treatment and other service costs for all homeless individuals. At least two states are using their state share of Medicaid for supportive housing. States and communities are also addressing the need to pay for PSH through Pay for Success initiatives (sometimes called Social Impact Bonds).
Chronically homeless individuals are those who spend long periods of time living on the street or other places not meant for human habitation, and who have one or more disabilities, frequently including mental illnesses and substance use disorders. In the 2015 Department of Housing and Urban Development (HUD) point-in-time count of people experiencing homelessness, more than 83,000 individuals met the definition of chronically homeless, down from nearly 120,000 in 2008. In part the decline is due to the federal government's plan, announced in 2002, to end chronic homelessness within 10 years. The target date has since been extended to 2017. Among the federal programs focused on ending chronic homelessness are the HUD Homelessness Assistance Grants, the HUD and Veterans Affairs Supported Housing Program (HUD-VASH), and several HUD demonstration programs.
One of the reasons that federal programs have devoted resources to ending chronic homelessness is studies finding that individuals who experience it, particularly those with serious mental illness, use many expensive services often paid through public sources, including emergency room visits, inpatient hospitalizations, and law enforcement and jail time. Even emergency shelter resources can be costly. In addition to potential ethical reasons for ending chronic homelessness, doing so could reduce costs in providing assistance to this population.
For years, ending chronic homelessness was thought to be a multi-step process, with individuals receiving treatment for addictions and illnesses, perhaps while living in transitional or temporary housing, before being found capable of living on their own. However, the strategy for ending homelessness has changed, largely due to research pioneered by housing providers. Instead of requiring chronically homeless individuals to be "housing ready" by first addressing issues thought to underlie homelessness, the new strategy allows chronically homeless individuals to move into permanent supportive housing without preconditions. Permanent supportive housing (PSH) is not time-limited and makes services available to residents. A particular PSH, called Housing First, focuses on resident choice about where to live and the type and intensity of services and does not require abstinence or medication compliance. Housing First has been embraced by HUD and the Department of Veterans Affairs as a way to end chronic homelessness.
Many researchers have examined PSH, including Housing First, as a way to reduce homelessness. Some researchers have also examined related outcomes, including changes in the use of services, and the costs of those services, by formerly homeless individuals after they move into housing; whether drug and alcohol use decreases; if there are improvements in mental health outcomes; and resident satisfaction after moving to housing. Overall, based on a review of the research, PSH helps increase days spent in housing and reduce days spent homeless, showing that PSH can be a successful way to end homelessness. The outcomes in other areas are not as clear, perhaps evidence that reductions in service use and costs, reductions in substance use, and mental health improvements may depend on individual needs and circumstances and require more than a successful move out of homelessness.
When reductions in service use result from chronically homeless individuals moving into PSH, any commensurate cost reductions are largely seen in public spending on health care. Medicaid funds can be used to pay for housing-related services, and increasingly housing advocates are encouraging this as a way to help chronically homeless individuals gain and maintain housing. In addition, with limited funding available for new units of housing through HUD programs, some states are using their own shares of Medicaid funds to finance permanent supportive housing for chronically homeless individuals. Another possible funding source is Pay for Success initiatives, where private investments in PSH are paid back if certain outcomes are attained.