The following statistics indicate the approximate average number of homeless people at any one time. Each country has a different approach to counting homeless people, so comparisons should be made with caution.
In the United States in the 1980s, homelessness became an important political topic and is widely assumed to have risen dramatically at this time. However, it is very difficult to prove this assumption, because data for previous years is almost completely non-existent. It is not certain to what extent this new focus on homelessness represents an increase in the extent of the problem, or an increase in public awareness of a condition that had always existed without comment.
Attempts to measure homelessness are often saddled with difficulties of ascertainment, definition, and methodology. There is no obvious direct way to count people who are defined as being 'not in a home'. Indirect methods, such as counting people who sleep in shelters or who eat at soup kitchens, provide estimates that can vary widely in degree of accuracy. Additionally, the definition of homelessness can be broadened to include, for example, a man who sleeps on a friend's couch until he finds a place of his own. Methodological questions such as, should a person who is homeless just one night in the year be included in the annual total, can also cloud the issue.
There are numerous possible causes of homelessness. Some people claim the problem is due to inadequate social services such as public housing. Some studies suggest rent control and other housing regulations create homelessness by reducing the supply of housing. Social changes, such as the movement to recognize the rights of those considered mentally ill, could lead to increased homelessness, as such people can no longer be arbitrarily rounded up and committed to mental hospitals. Such a change occurred in the United States in the early 1980s, where it is now estimated that one-third of homeless persons have some form of mental illness. Substance abuse may be a cause as well - an estimated other third of America's homeless have substance abuse problems.
Traditionally single men have constituted the overwhelming majority of the homeless. In the 1980s there was a sharp rise in the number of homeless families in certain parts of the United States (notably New York City). Most homeless families consist of an unmarried mother and children.
Sometimes the term urban outdoorsman is used as a euphemism for a homeless man.