18 years. In the case of parental death, intact families were right-censored at offspring age when their parent(s) died. Post-hoc tests of interactions between parental separation and parental substance dependence were also conducted. The Efron approximation (Efron, 1977) was used for survival ties. To examine potential violation of the PH assumption, the Grambsch and Therneau test of Schoenfeld residuals (Grambsch and Therneau 1994) was employed, with age-interactions modeled to correct observed violations (Cleves et al., 2004).
