Over the past two decades, empirical and conceptual work has resulted in an ecological developmental framework for understanding and preventing aggression in childhood and adolescence. In this framework, individual and environmental risk processes launch some children onto a developmental trajectory characterized by increased and, ultimately, chronic use of aggression and violence. The framework suggests a need to examine further the course of aggression into early adulthood and the dynamic nature of relationships between risk and aggression.

Based on this framework, this study used semiparametric group-based modeling (SGM) to identify (a) trajectories of aggression, (b) trajectories of risk, and (c) dual trajectories of aggression and risk in a representative sample of 1,227 participants in Waves 1 to 7 of the National Youth Survey (NYS). Participants were between ages 11 and 17 (M = 13.8 years) at Wave 1 and were followed over a 10-year period. Background information was collected from caregivers at baseline, and participants completed self-report measures of risk and protective factors and behavior over 7 Waves.

Results revealed 5 aggression trajectories: low-stable; early onset-stable; early onset-desister; adolescent onset; and adult onset. Males were more likely to be in trajectory groups with high or increasing aggression; however, race/ethnicity and family socioeconomic status were not significant predictors of trajectory group membership.

Trajectories of risk varied by domain. For example, 4 trajectories described exposure to delinquent peers (EDP): high-stable, low-stable, low baseline-moderately increasing, and moderate baseline-decreasing. In contrast, 7 trajectories described lack of involvement in conventional activities. 2 groups were low risk at baseline, and risk remained low for 1 group but increased for the other. 3 groups were at midrange at baseline; risk decreased for 1, remained stable for a second, and increased for the third. Risk remained stable for 2 additional groups, one with moderately high baseline risk and the second with high baseline risk.

Results of dual trajectories included estimated joint probabilities of group membership, shedding light on dynamic relationships between risk and aggression. For example, members of the early onset-stable and early onset-desister aggressions groups differed with respect to EDP over time. The probability of membership in the early onset-stable aggression group, given membership in the high-stable EDP trajectory was relatively high, .54, suggesting this risk factor was related to high levels of aggression throughout adolescence and early adulthood. The probability of membership in the early onset-desister trajectory, given membership in the high-stable EDP trajectory was low, .04, but the probability of membership in this aggression trajectory given membership in the moderate baseline-decreasing EDP trajectory was higher, .49, indicating that decreasing exposure to delinquent peers over time acted as a protective factor, well into adolescence, for participants who displayed initially high levels of aggression.

Implications of the results for understanding dynamic relationships between risk and aggression will be discussed, with an emphasis on using this information to develop prevention programs that strategically target risk and protective factors based on aggression and risk profiles and developmental levels.