effects due to cocaine use and that received treatment were intermediate between Groups 3 and 5. The heritability of Group 4 was 0.66 (SE = 0.05). The 1,916 subjects in Group 5, the early-onset, heavy cocaine use, high comorbidity group, had the highest prevalence of substance dependence and psychiatric disorders. This group reported the earliest onset of cocaine use (17.9 years, SD = 4.3) and of heaviest use (25.8 years, SD = 8.4), and endorsed a high rate of adverse effects of cocaine use (Table III). The heritability of Group 5 was 0.64 (SE = 0.05). Because of the high prevalence of CD, Groups 4 and 5 were chosen as the most clinically informative subtypes of CD and were compared with DSM-IV CD as traits for association analysis.
