We examined age at first voluntary sexual intercourse in a birth cohort of African and European ancestry female twins, employing both survival-analytic and propensity score approaches to identify unique effects of parental separation above and beyond parental alcoholism and other correlated risk-factors. Consistent with prior research [9], in families of European ancestry, risk associated with parental separation was observed throughout adolescence in Cox regression models. Although likelihood of sexual onset was highest in separated alcoholic families, compared to intact nonalcoholic families, twins of nonalcoholic parents who separated also reported earlier first sex even controlling for sociodemographic characteristics, parent and offspring psychopathology, and childhood abuse. Results of propensity score analyses comparing intact and separated families matched on predicted probability of parental separation largely confirmed the specificity of risk from parental separation. Parental separation was associated with early-onset sex across quintile of predicted probability of separation. Likewise, twins whose parents remained together were at reduced risk even in the highest quintile of predicted probability of parental separation, where we observed increased rates of parental alcoholism in both intact and separated families.
