Parsing between- and within-person effects: Longitudinal associations between irritability and internalizing and externalizing problems from early childhood through adolescence

This report examines between- and within-person associations between youth irritability and concurrent and prospective internalizing and externalizing symptoms from early childhood through adolescence. Distinguishing between- and within-person longitudinal associations may yield distinct, clinically relevant information about pathways to multifinality from childhood irritability. Children's irritability and co-occurring symptoms were assessed across five waves between ages 3 and 15 years using the mother-reported Child Behavior Checklist ( 605, 46% female). Parental history of depressive disorders was assessed with a clinical interview. Results demonstrated that between- and within-person irritability were uniquely associated with concurrent depressive, anxiety, and defiance symptoms, but not ADHD. Prior wave within-person irritability also predicted next wave depressive, anxiety, and defiance symptoms, controlling for prior symptoms; these prospective associations were bidirectional. Child sex and parental depressive disorders moderated associations. Findings identify pathways from within- and between-person irritability to later internalizing and externalizing psychopathology. Results demonstrate the importance of parsing within- and between-person effects to understand nuanced relations among symptoms over childhood.