Participants and their parents were interviewed separately for symptoms of psychopathology by trained interviewers with at least a B.A. in Psychology. Lifetime criteria of attention-deficit/hyperactivity disorder (ADHD) and oppositional defiant disorder (ODD) were assessed in adolescents via a modified version of the Diagnostic Interview for Children and Adolescents - Revised, parent version (DICA-R-P; Herjanic & Reich, 1982; Reich & Welner, 1988). In almost all cases, the twins’ mother was the parent informant on the DICA-R-P. Adolescents were independently interviewed using the child version of the same diagnostic interview (DICA-R-C) to assess lifetime criteria of ADHD and ODD. Adolescents were administered the Structured Clinical Interview for DSM-III-R Personality Disorders (SCID-II; Spitzer, Williams, Gibbon, & First, 1987) to assess symptoms of conduct disorder. A modified version of the expanded Substance Abuse Module of the Composite International Diagnostic Interview (Robins et al., 1988) was used to assess lifetime criteria of alcohol dependence.
