Interestingly, the moderating effects that we found on behavior problems in early adolescence largely parallel the effects we reported previously with alcohol use in older adolescents. Genetic influences on behavior problems at age 12 were more important in urban settings, whereas common environmental influences assumed greater importance in rural settings. These findings are exactly what have previously been reported for alcohol use in later adolescence in a slightly older Finnish twin sample (Rose et al., 2001b). Interestingly, a replication of the urban/rural interaction in the Minnesota twin sample expanded the phenotype to incorporate both substance use and rule-breaking behavior (symptoms of conduct, oppositional defiant, and antisocial personality disorders) at age 17 (Legrand et al., 2007). Additionally, we find that genetic influences assume greater importance on behavior problems at age 12 in neighborhoods with a larger percentage of slightly older adolescents (ages 15 to 19), parallel to the effect reported for alcohol use at age 18 with slightly older young adults (ages 20 to 24; grouping predetermined by SuomiCD statistics). The fact that we find parallel moderation effects associated with neighborhoods
