Among AA families, prevalence of parental separation ranged from 38% (0-20%ile of propensity score distribution) to 100% (>80%ile of propensity score distribution). Within-quintile comparisons of AA family background characteristics are presented in Table 6, with results of a multivariate model predicting parental separation provided in Table S34. As shown, imperfect matching is especially evident for parental (maternal or paternal) alcoholism, where a high proportion of alcoholic families fell into the highest quintile of separation risk, where there was no counterfactual, i.e., no stably intact families with an alcoholic parent. Similarly, for maternal age at twins’ birth, there were no stably cohabiting or married mothers who gave birth as teens. Consequently, within-quintile comparisons of twin substance involvement by parental separation were not conducted.
