The characteristics of the study participants are listed in Table 1. The sample is 68% European American and 32% African-American. Comorbid substance dependence is common, with over half of the subjects dependent on any given substance being dependent on at least one other substance as well. The extent of comorbidity in these data is illustrated in Figure 1. Demographics broken down by ethnic subgroups can be found in Supplemental Table S1. Rates of substance use and rates of dependence among those who have used are shown in Supplemental Table S2. We define use of cigarettes as having smoked at least 100 cigarettes lifetime (a common definition). For the other substances, use is defined as having tried it at least once. Each study’s demographic characteristics are consistent with its recruitment design.
