Data were collected by telephone by trained interviewers. At baseline, a screening to determine zygosity of the twin pair was conducted with one of the twins’ parents. Parental diagnostic interviews were then scheduled and conducted after verbal consent was obtained. Interviews with the twins were conducted after obtaining verbal consent (and parental consent for those under the age of 18). The same protocol was followed in Waves 3 and 4. An interview modified for telephone administration from the Semi-Structured Assessment for the Genetics of Alcoholism (SSAGA/SSAGA-II ; Bucholz et al. 1994; Hesselbrock et al. 1999) was used to assess trauma history, early childhood home environment, and DSM-IV diagnoses, including PTSD and AD.
