Structured diagnostic interviews based on the Semi-Structured Assessment for the Genetics of Alcoholism (SSAGA; Bucholz et al., 1994; Hesselbrock et al., 1999) were administered by telephone with mothers and offspring during 2003–2004. Experienced staff at the Institute for Survey Research at Temple University recruited participants and collected all data. Interviewers were blind to the drug dependence status of the fathers and co-twins. Fathers were interviewed first and provided permission to contact the offspring and the biological mother of the offspring for interviews. All participants (fathers, co-twins, mothers, and offspring) gave verbal consent before participating in the interview. The period of interview, target population (twins, mothers, and child) and primary assessment are shown in Figure 1.
