Group 1 was the largest, consisting of 3,370 subjects (56.5% women), none of whom had a diagnosis of CD. Group 1 had a mean of 3.8 (SD = 3.1) reported lifetime episodes of cocaine use and the lowest prevalence of all other substance dependence and psychiatric disorders (except ASPD, which was slightly lower in Group 3). The estimated heritability of the non-cocaine use group was 0.41 (SE = 0.06). Group 2, comprised of 1,241 subjects, had a significantly lower rate of CD (62.1%) and was less likely to have comorbid dependence on nicotine, alcohol, sedatives, or stimulants and psychiatric disorders (except ASPD) than groups 3–5. Of the cocaine-use groups, Group 2 had the lowest percentage of individuals reporting daily or almost daily cocaine use, negative effects due to cocaine use, and a history of cocaine treatment, but a higher rate of intravenous cocaine injection (31.3%) than Groups 3 (24.4%) or 4 (3.9%). Group 2 had the highest estimated heritability (0.69, SE = 0.05).
