Wave 1 participants 2 years after Wave 1 was completed. (Data were not drawn from Wave 2 assessments as they did not cover all domains of interest for this study and referenced experiences from only the previous 24 months.) All twins from the target cohort (excluding those who had asked not be recontacted) were contacted for Wave 4 interviews, which were conducted from 2002 to 2005. (Approximately 83 % of Wave 1 participants took part in Wave 4. Attrition was not related to history of childhood trauma.) PTSD diagnoses were collected only at Wave 4, but trauma exposure and AD diagnoses were also assessed in Waves 1 and 3. Lifetime trauma and AD status were established using data from all available waves of data collection (78% of the sample had participated in Wave 1 and/or Wave 3). Mean age at the time of Wave 4 interviews was 21.7 years (s.d.=2.7, range=18–29). Eighty-five per cent of the sample self-identified as Caucasian, 15 % as African-American.
