Measurement and Correlates of Irritability in Clinically Referred Youth: Further Examination of the Affective Reactivity Index

Abstract Background: Research on youth irritability has proliferated in recent years, largely facilitated by items from existing measures and by key new instruments like the Affective Reactivity Index (ARI). The present study extends this literature by investigating the psychometric properties of the parent- and youth-report ARI and the correlates of irritability in an independent, clinically referred sample. Method: Baseline assessment data were collected from 237 youths (ages 3-18; 36% female) and their parents, seen for outpatient therapy and/or assessment. We examined the ARI in terms of (1) its item, scale, and factor properties; (2) convergent/discriminant validity with internalizing, externalizing, and emotion regulation problems; (3) specificity of associations with reactive aggression, anger, dysregulation, and coping; and (4) robustness of associations after controlling for demographic variables (e.g., age, gender). Results: The ARI's internal consistency and unidimensional factor structure were acceptable or better, with some variation across items and informants. Irritability, as measured by parent- and youth-report, was associated with variables in the externalizing (inattention, hyperactivity, executive dysfunction, aggression), internalizing (anxiety, depression, suicidality), and emotion regulation domains. Associations with reactive aggression, anger, dysregulation, and coping problems were especially pronounced. Irritability's links with internalizing and externalizing problems remained robust after controlling for demographic covariates. Limitations: The sample was limited in diversity and moderate in size. Conclusions: Findings support the reliability and validity of the ARI for assessing parent- and youth-rated irritability among clinically referred youth. Future research is needed to understand variations in irritability's manifestations, measurement, and correlates across demographic groups.