http://www.ashevillenc.gov/Portals/0/city-documents/planning/homeless/National%20Law%20Center%20Myths%20and%20Facts.pdf
Substance Abuse and Mental Illness

Myth: All homeless people are mentally ill or substance abusers.
Fact: Around a quarter of homeless people are mentally ill, and about 40% are alcohol or substance abusers, with around 15% suffering both disabilities.
Koegel has researched the prevalence of mental illness among the homeless population and found "between 20% and 25% of those homeless people studied have at some time experienced severe and often extremely disabling mental illnesses such as schizophrenia and the major affective disorders (clinical depression or bipolar disorder)."9
James Wright, of Tulane University, has studied the prevalence of alcohol and other drug abuse among the homeless population. He finds that 38% of homeless people are alcohol abusers, as opposed to 10% of the general population. He furthermore finds that 13% of homeless people are drug abusers.10
The Center for Mental Health Services states that betweeen10 and 20% of homeless people suffer "co-occurring severe mental and substance use disorders."11 

• Homeless Population Demographics
  Myth: Homeless people are mostly single men.
  Fact: Families constitute a large and growing percentage of the homeless population.
  A recent study found that families comprise 38% of the urban homeless population.5 Other research finds that homeless families comprise the majority of homeless people in rural areas.6
  
  Employment
  Myth: Homeless people don't work and get most of their money from public assistance programs.
  Fact: Homeless people do work, and a relatively small percentage of them receive government assistance.
  A nationwide study by the Urban Institute in 1987 found that only 20% of 1,704 homeless people received AFDC, GA, or SSI.7 
  
  
  
  The Chronic Theory
  Myth: Homeless people are a fixed population who are usually homeless for long periods of time.
  Fact: The homeless population is quite diverse in terms of their length of homelessness and the number of times they cycle in and out of homelessness.
  Research on the length of homelessness states that 40% of homeless people have been homeless less than six months, and that 70% of homeless people have been homeless less than two years.3 
  
  

  • transitionally homeless who have a single episode of homelessness lasting an average of 58 days,
    
  • episodically homeless who have four to five episodes of homelessness lasting a total of 265 days,
    
  • chronically homeless who have an average of two episodes, lasting a total of 650 days.4 
    
    
    references 
    
    
    1. James Wright, Memo to NLCHP: Transiency of Homeless Substance Abusers 1 (March 11, 1997)
       
    2. Martha Burt, What We Know About Helping the Homeless and What It Means For HUD's Homeless Programs
       Testimony presented to the Housing and Community Development Subcommittee of the Banking and Financial
       Institutions Committee of the U.S. House of Representatives 1 (March 5, 1997).
       
    3. Dennis Culhane, Testimony presented to the Housing and Community Development Subcommittee of the Pamela
       Fischer, Criminal Activity Among the Homeless: A Study of Arrests in Baltimore 49 (January, 1988).
       
    4. Banking and Financial Institutions Committee of the U.S. House of Representatives, Figure 3 (March 5, 1997).
       
    5. U.S. Conference of Mayors, A Status Report on Hunger and Homelessness in America's Cities:1996 (1996)
       
    6. Yvonne Vissing, Out of Sight, Out of Mind: Homeless Children and Families in Small Town America, 1996 (1996).
       
    7. Martha Burt and Cohen, America's Homeless: Numbers, Characteristics, and Programs that Serve Them 43 (1989).
       
    8. Peter Rossi, Down and Out in America 40 (1989).
       
    9. Paul Koegel, Causes of Homelessness, Homelessness in America 31 (1996).
       
    10. James Wright, Homelessness and Health 68 (1987).
        
    11. Substance Abuse and Mental Health Services Administration, Center for Mental Health Services, U.S. Department of
        Health and Human Services, Integrating Mental Health and Substance Abuse Services for Homeless People with Co- Occurring Mental and Substance Use Disorders 1.