Present analyses were based on parent interviews and Waves 1, 3, 4 and 5 twin interviews. Twins were selected if they had data on voluntary sexual intercourse and both parental separation and parental alcoholism described below. We excluded 11 twins (6 AA, 5 EA) reporting onset of voluntary sex prior to age 12 (on the presumption that sex at ages 11 and younger is likely to involve coercion even if reported as voluntary [21]), leaving a sample of 3984 twins (569 AA, 3415 EA) from 2088 families (304 AA, 1784 EA). Propensity score analyses were based in part on maternal ratings of alcohol problems and therefore limited to 1568 twin-families (187 AA, 1381 EA) with maternal data. At last assessment of voluntary sex, twins ranged in age from 15 (Wave1) to 29 (Wave 4) years. Additional sample characteristics are provided in Table S1, separately by race/ethnicity and presence/absence of parental separation and parental alcoholism.
