Measurement Invariance of the Affective Reactivity Index Across Five Countries

Objective Irritability is a globally relevant dimension of youth psychopathology, yet cross-national comparisons require evidence that assessment tools function equivalently across countries and languages. We examined the reliability, factor structure, and measurement invariance of the Affective Reactivity Index (ARI) across Brazil, China, Japan, Spain, and the United States (US). Method Community samples (N = 6,195; ages 6–18 years) completed parent- or youth-report ARI versions. Single-factor confirmatory factor analyses evaluated model fit and internal consistency. Multi-group CFA tested measurement invariance across countries. Where invariance was supported, cross-country differences and age and sex associations were examined. Results Internal consistency was acceptable to good across countries and informants. A single-factor structure was broadly supported. For parent report, measurement invariance was established across China and Japan using the original response format and across China, Japan, and the United States when items had to be dichotomized due to lack of endorsement of the highest category in item 4 by US parents. For youth report, threshold and loading invariance were supported, but scalar invariance was not, indicating cross-country differences in intercepts. Parent-reported irritability was higher in China and Japan than in the United States, whereas youth-reported irritability was highest in Brazil. Parents reported higher irritability in boys and younger youth; youth self-report showed no significant age or sex effects. Conclusion The ARI captures a broadly comparable irritability construct across countries, particularly for parent report. Cross-national mean comparisons using youth report should be interpreted cautiously. Establishing measurement invariance is essential for valid international research on pediatric irritability.