I attended Psychiatry Grand Rounds a few weeks ago for a talk by Dr. Carole North, a psychiatrist who is probably most famous as an epidemiologist. She has done several studies looking at the homeless population.
I won't go through every aspect of her talk, but will provide a few fun facts here:
Substance abuse accounts for most of the mental illness in the homeless population. It is also hypothesized that increased rates, since 1980, of bipolar disorder and schizophrenia may be related to the effects of continued use of crack cocaine.
The rate of non-substance abuse mental illness in the homeless population is not nearly as high ("50% of the homeless are schizophrenics!") as is commonly thought. The rate of schizophrenia is around 6% - schizophrenia affects around 1% of the general population. In 1990 in St. Louis, depression was highest, but even this was related to what Dr. North termed 'misery' - higher in men, and most likely associated with having to be out in the elements on days of harsh weather.
African-American men who are homeless are more likely to be younger, have jobs, and still make less income than Caucasian men who are homeless.
Women are most likely (around 20%) to be homeless because of family conflicts.
Of those who are substance abusers, most use cocaine (including crack), and they typically do not use money from government assistance or income from jobs to buy drugs. No, by a large percentage, they use the money they get from panhandling, and in some cases make up a disproportionate number of panhandlers. So know that when you give money to panhandlers, there's a good chance it will be used to buy drugs. As Dr. North stated at the end of her talk, she gives money to shelters and other services for the homeless, but not to panhandlers.
Only two people, out of nearly 900 in one of her studies, said that they chose to be homeless.