test indicated that the addition of a third class would not result in significant improvement in model fit (P=.52). The Figure depicts these 2 GMM-estimated externalizing trajectories. Most of the sample displayed a developmentally limited pattern of externalizing behavior (83.1%), peaking at or before the initial wave of assessment (at 12 years of age), with a steady linear decline thereafter (βintercept=11.1, P<.001; βslope=−0.54, P<.001). A smaller proportion of the sample (16.9%) had higher initial levels of externalizing behavior that persisted across the period from early adolescence into young adulthood (βintercept=16.8, P<.001; βslope=0.04; P=.79 [not significant]). Table 3 displays results of a series of 2-class GMMs wherein trajectory class membership was regressed on genotype. Findings demonstrate that adolescents' odds of membership in the elevated persistent externalizing trajectory increased with each additional copy of the minor allele. For example, for rs497068, the first SNP listed in the table, 9.3% of individuals carrying no copies of the minor allele displayed elevated persistent antisocial behavior, 15.2% of individuals carrying 1 copy of the minor allele displayed elevated persistent externalizing behavior, and 21.1% of individuals carrying 2 copies of the minor allele displayed elevated persistent externalizing behavior. Corresponding odds ratios ranged from 2.1 to 2.7
