Interview Schedule (DIS-III-R; Robins, 1989) in which DSM-III-R alcohol abuse and dependence, drug abuse and dependence and psychiatric disorders were assessed (Tsuang et al., 1996, 1998). Beginning in 2002, twins were recruited into the OOT study based on 3 selection criteria: (i) both members of the twin pair completed the 1987 mailed questionnaire and the 1992 telephone interview, (ii) at least one member of the twin pair had a child born between 1973 and 1987, and (iii) at least one member of the twin pair met criteria for DSM-III-R lifetime illicit drug dependence based on data from the 1992 structured interview. Twin pairs were identified as concordant or discordant for lifetime history of illicit drug dependence. Control twin pairs with no history of drug dependence were also identified.
