Seena Fazel and colleagues of the University of Oxford identified 29 studies involving 5,684 homeless individuals in the United States, Britain, Europe and Australia. Combining the data from the surveys, the researchers determined the prevalence of serious mental disorders was raised compared with expected rates in the general population.

The most common mental disorders appeared to be alcoholism at 37.9 percent and drug abuse at 24.4 percent. The review also found the rate of alcohol abuse has increased in recent decades.

The prevalence estimates for psychosis were found to be as high as those for depression, which contrasts with community estimates and other "at-risk" populations such as prisoners and refugees in which depression is more common, the researchers said.

The meta-analysis was published in the journal PLoS Medicine.