History of voluntary sexual intercourse, including age of onset, was assessed of twins aged 16 and older at Wave 1 and all twins at Waves 3 and 4. Twins were asked, “Have you ever had sexual intercourse (other than when you were forced)?” and for those responding affirmatively, “How old were you when you first had sexual intercourse (other than when you were forced)?” Youngest reported age at first voluntary sexual intercourse was coded for twins with multiple reports across assessment waves; however, youngest and first report were highly correlated (r=0.98, p<0.05). History of forced sexual intercourse during childhood was coded separately as sexual abuse and included among control variables described below.
