Both cohorts completed interviews based on the Semi-Structured Assessment for the Genetics of Alcoholism (Bucholz et al., 1994). The Cohort II assessment was administered by telephone and the Cohort III assessment was administered using a computer-assisted telephone interview. Retest data were collected 3.7 years (standard deviation (SD)=0.4, range=1.1–4.3) after the interview for a subsample of twins (n=216) from Cohort II. Interviews were conducted by trained lay-interviewers who were blind to the status of the co-twin. Informed consent was obtained from participants and the study was approved by the Institutional Review Boards at Washington University School of Medicine, the University of Missouri, and the Queensland Institute of Medical Research.
