Peer deviance, parental knowledge/monitoring, and stressful life events are three of the candidate environments that have been examined by multiple groups as moderators in the area of adolescent externalizing behavior (e.g., alcohol and drug use and conduct problems). A number of these studies found evidence that these factors significantly moderate genetic influences on alcohol use. Dick, Pagan, et al. (2007) found that peer alcohol use moderated the heritability of adolescent alcohol use. They demonstrated that when more peers are using alcohol, the genetic influence on the adolescent’s alcohol use is greater. Similarly, Harden et al. (2008) found that the effect of a best friend’s substance use is dependent on the target adolescent’s genetic liability; those adolescents with greater genetic liabilities toward substance use were more strongly affected by their best friend’s substance use. With regards to parental monitoring, Dick, Viken, et al. (2007), using the classic univariate moderation model, showed that genetic influences on adolescent substance use were greater at lower levels of parental monitoring. In addition, Miles et al. (2005) found a moderating effect of parental characteristics on adolescent
