Twins were selected from Cohort II if they had data on lifetime DSM-IV AD symptoms and variables used to code reproductive onset, both assessed during interview. Of 6257 interviewed twins, 6129 (98%) had data on both AD and reproductive onset, including 3381 female and 2748 male respondents. Age at interview of selected twins ranged from 22 to 36 [M (SD) = 30.42 (2.45)].
