Alcohol, nicotine (any form), cannabis, and any illicit drug dependence phenotypes were defined according to lifetime DSM-III-R criteria. Any illicit drug dependence combined separate assessments of cannabis, cocaine, stimulants, sedatives, opiates, and hallucinogens/PCP (asked of individuals who used a substance more than 5 times). All substance dependence diagnoses were based on the 1992 telephone diagnostic interview.
