Does Marriage Inhibit Antisocial Behavior? An Examination of Selection vs Causation via a Longitudinal Twin Design

Context: Previous studies have indicated that marriage is negatively associated with male antisocial behavior. Although often interpreted as a causal association, marriage is not a random event. As such, the association may stem from selection processes, whereby men less inclined toward antisocial behavior are more likely to marry. Objective: To evaluate selection vs causation explanations of the association between marriage and desistence from antisocial behavior. Design: Co-twin control analyses in a prospective twin study provided an analogue of the idealized counterfactual model of causation. The co-twin control design uses the unmarried co-twin of a married twin to estimate what the married twin would have looked like had he remained unmarried. Discordant monozygotic (MZ) twins are particularly informative because they share a common genotype and rearing environment. Setting: General community study. Participants: Two hundred eighty-nine male-male twin pairs (65.1% MZ) from the Minnesota Twin Family Study underwent assessment at 17, 20, 24, and 29 years of age. None of the participants were married at 17 years of age, and 2.6% were married at 20 years of age. By 29 years of age, 58.8% of the participants were or had been married. Main Outcome Measure: A tally of criterion C symptoms of DSM-III-R antisocial personality disorder, as assessed via structured clinical interview. Results: Mean differences in antisocial behavior across marital status at age 29 years were present even at 17 and 20 years of age, suggesting a selection process. However, the within-pair effect of marriage was significant for MZ twins, such that the married twin engaged in less antisocial behavior following marriage than his unmarried co-twin. Results were equivalent to those in dizygotic twins and persisted when controlling for prior antisocial behavior. Conclusions: Results indicate an initial selection effect, whereby men with lower levels of antisocial behavior are more likely to marry. However, this tendency to refrain from antisocial behavior appears to be accentuated by the state of marriage.