Prevalence of dual diagnosis in community-based day programs in the Chicago metropolitan area.

A two-step methodology was used to estimate the prevalence of dual diagnosis among persons participating in community-based day programs in the Chicago metropolitan area. In Step 1, a dual diagnosis screening test was administered to a random sample of 205 people with mental retardation. In Step 2, 59 subjects were evaluated by clinical psychologists who did not know the results of the screening test. The results consistently suggested very high rates, with the best data suggesting an overall rate of about 39%. The rates were high primarily because personality disorders were very common. The fact that only 11.7% of the subjects had a psychiatric diagnosis in their case files suggests that dual diagnosis was underdiagnosed for this sample.