Aggression and Irritability in Middle Childhood: Between- and Within-Person Associations.

Objective: This study tested predicted bidirectional associations between irritability and physical and relational forms of aggression, disentangling theorized within- and between-person effects using latent curve models with structured residuals (LCM-SR) over one year in middle childhood. Gender differences and robustness of results when controlling for other externalizing problems (i.e., attention problems, delinquency) were also considered.

Method: Children in third, fourth, and fifth grade (N = 704, 49.9% female) were recruited from schools in a large midwestern city. The sample was diverse in regard to race/ethnicity (31% Black, 29% White, 13% Hmong, 14% Latinx, 4% Native American, 4% Asian, 5% other races/ethnicities). Irritability, attention problems, and delinquency were measured using teacher-report, and physical and relational aggression were measured using self-report at three time points over one calendar year.

Results: At the between-person level, higher mean levels of irritability predicted higher initial levels of physical and relational aggression. Irritability continued to predict higher levels of physical aggression across the course of the study, whereas the effect of irritability on relational aggression diminished. Boys showed higher starting levels of physical aggression, but no other significant gender differences emerged. No significant within-person associations were found.

Conclusions: The present study suggests that irritability may represent a between-person risk factor for high levels of physical and relational aggression in middle childhood, although effects on physical aggression may be more persistent. This highlights the importance of considering affective processes to understand the development of aggression trajectories.