Data were collected via telephone interview using an adaptation of the Semi-Structured Assessment for the Genetics of Alcoholism (Bucholz et al., 1994; Hesselbrock et al., 1999), which assesses Diagnostic and Statistical Manual of Mental Disorders (DSM)-IV (American Psychiatric Association, 2000) psychiatric disorders, history of substance use, and related psychosocial constructs. The study was carried out in accordance with the latest version of the Declaration of Helsinki and approved by the Washington University School of Medicine Human Research Protections Office. Prior to participation, informed consent was obtained from all twins 18 years of age or older, as were parental consent and twin assent for twins under age 18.
