Behavioral genetic research has argued that differential twin perceptions of an objectively shared or family-wide event can yield effectively nonshared or child-specific child outcomes, whereby only one twin engages in more pathological behavior as a consequence of this shared experience. However, prior research has yet to resolve the extent to which their findings were due to differential perceptions of a shared event or exposure to nonshared events. The current study sought to address this issue by examining whether differential perceptions of a family-wide experience (i.e., marital conflict) can have effectively nonshared outcomes (i.e. differential externalizing). Participants included 500 population-based twin families and 174 high-risk twin families from the Twin Study of Behavioral and Emotional Development in Children (TBED-C). The Children's Perceptions of Interparental Conflict inventory (CPIC; Nigg et al., 2009) was used to assess twin-specific perceptions of interparental conflict. The Child Behavior Checklist (Achenbach & Rescorla, 2001) was used to measure externalizing behaviors in each twin. Analyses were conducted using both a monozygotic twin differences design and co-twin control design, a statistically powerful counterfactual approach for identifying nonshared environmental mediation (McGue, Osler, & Christensen, 2010). Discordance in twins' perceptions of their parents' conflict did not predict discordance in their externalizing behaviors in either set of analyses. Such findings are not consistent with the notion that objectively shared events often have effectively nonshared effects on outcome.
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