These analyses use data collected in the third wave of assessment of adult Caucasian male twins participating in the Virginia Adult Twin Study of Psychiatric and Substance Use Disorders (Kendler & Prescott, 2006). Subjects (n=1790) were aged 40.27 (S.D.=9.00) years at the interview. Data were available for 466 complete monozygotic (MZ) twin pairs, 283 complete dizygotic (DZ) twin pairs, and 292 members of incomplete pairs. Zygosity was determined using a combination of self-report measures, photographs and DNA polymorphisms. Most subjects were interviewed over the telephone by interviewers with a Master’s degree in a mental health-related field or a Bachelor’s degree and at least 2 years of clinical experience. The Committee for the Conduct of Human Research at Virginia Commonwealth University approved the project.
