613 unrelated proband individuals from the group of interviewed subjects were offered participation in this genetic study, based on the availability of screening resources. No individual who was offered participation during this time period refused to participate. The individuals who accepted participation averaged age 34 and were 72% male, 72% African American, 26% European-American and 2% of other ethnicities, based on self-report. Subjects accepting research participation in this study thus appear representative of this overall research volunteer population in this area. They also share some characteristics of the drug abusing population in Baltimore, based on population trends and 1981 data from the Baltimore Epidemiological Catchment Area (ECA) site that identified 57% of the males and 41% of the females who displayed substance abuse and/or dependence as European-American (J. Anthony, personal communication, 1998).
