History of voluntary sexual intercourse was reported by 84% and 77% of AA and EA twins, respectively, with AA twins younger on average at first sex (M[SD]=16.85[2.57] years) than EA twins (M[SD]=17.43[2.51] years, log-rank X21=32.22, p<0.0001). Seventy-four percent and 38% of parents of AA and EA twins had separated, with AA twins younger at parental separation (M[SD]=3.64[4.85] years) than EA twins (M[SD]=5.89[5.07] years, log-rank X21=415.44, p<0.0001). Either or both parents were more likely to be coded positive for alcoholism in AA compared to EA families (41% versus 35%, X21=8.58, p<0.05).
