The Nonlinear Interaction Effects of Negative Emotions and Self-Control on Developmental Trajectories of Early Adolescents' Internalizing Problems.

Negative emotions and self-control have long been considered important predictors of adolescents' internalizing problems. While numerous studies examining the linear interaction between negative emotions and self-control on internalizing problems have produced inconsistent findings, emerging evidence indicates these two factors may exert nonlinear interaction effects on distinct trajectories of the problems. This study aimed to identify the developmental trajectories of adolescents' internalizing problems and employ polynomial regression and response surface analysis to explore the nonlinear interaction effects between negative emotions and self-control on these trajectories. A total of 639 students were recruited, and 619 valid participants were retained for three longitudinal assessments (Mage =14.03, SDage = 0.37 at time 1; 47.2% female), using 1-year intervals in between. Results revealed three trajectories: low-decreasing (80.45%), moderate-increasing (14.86%), and high-decreasing (4.69%). The nonlinear interaction effects of negative emotions and self-control on internalizing problems were significant for adolescents within the low-decreasing and moderate-increasing trajectories, but not significant within the high-decreasing trajectory. Specifically, in the low-decreasing trajectory, an inverted U-shaped nonlinear effect was observed, with lower predicted internalizing problems at greater levels of incongruence, whether negative emotions or self-control was higher. In the moderate-increasing trajectory, a tentative U-shaped nonlinear effect emerged at the congruence level of negative emotions and self-control, with moderate levels of both negative emotions and self-control predicting lower internalizing problems. These findings indicate that the nonlinear interaction effects between negative emotions and self-control may vary across internalizing-problem trajectories in early adolescence, highlighting the importance of accounting for developmental heterogeneity when examining risk and protective factors for youth internalizing difficulties.