The Affective Reactivity Index in Australian children: Psychometric properties and measurement invariance across clinical and community samples.

Irritability is a common transdiagnostic feature of child psychopathology, often first emerging in early to middle childhood.This study investigated the psychometric properties of the Affective Reactivity Index-Parent Version, a widely used measure of irritability, in Australian children aged 4-12 years.Participants were a community sample broadly representative of the general population on key demographic characteristics (n = 1,371; 47.05% female) and a clinic-referred sample of children with conduct problems and related comorbidity (n = 299; 23.7% female).Affective Reactivity Index-Parent Version scores demonstrated strong internal consistency, test-retest reliability, good convergent and concurrent validity, and high caregiver-rated acceptability.Metric, but not scalar, invariance was supported across community and clinical samples, whereas full scalar invariance was supported across early (4-7 years) and middle (8-12 years) childhood within the community sample.Psychometric network analysis identified a single symptom cluster in both samples, with Items 5 ("Gets angry frequently") and 6 ("Loses temper easily") emerging as most central.These findings support the Affective Reactivity Index-Parent Version as a reliable and valid tool for the assessment of irritability in young children and highlight its utility for both research and early identification across diverse settings. Public Significance StatementThis study found the Affective Reactivity Index-Parent Version to be a reliable, valid, and acceptable tool for the assessment of irritability in early to middle childhood, across both community and clinical settings.This is important because irritability is common in childhood and linked to a broad range of mental health problems across the lifespan.