Validation of an irritability measure in preschoolers in school-based and clinical Brazilian samples

The Affective Reactivity Index (ARI) is an irritability measure with good psychometric properties. However, there are no published studies in preschool children, an important population in which to differentiate normative from non-normative irritability. The goal of this study was to validate the ARI in preschoolers. Two samples were included: a school-based sample (N = 487, mean age = 57.80 ± 7.23 months, 52.8% male) and a clinical sample of children with Attention Deficit Hyperactivity Disorder (ADHD; N = 153, mean age = 60.5 ± 7.6 months, 83.7% males). Confirmatory factor analysis assessed ARI unidimensionality. ARI criterion validity was tested through comparison to other scales measuring irritability, related constructs, and other aspects of psychopathology. Test-retest reliability was assessed in the school-based sample. Analyses confirmed a single-factor structure and good internal consistency. The ARI showed stronger correlations with irritability measures than with measures of other constructs. In the clinical sample, ADHD children with comorbid disruptive behavior disorders had higher ARI scores than those without this comorbidity. In the school-based sample, test-retest reliability was moderate. This is the first study to demonstrate ARI validity and reliability in preschoolers. The scale performed well in both school-based and clinical samples. Having a concise and validated irritability measure for preschoolers may facilitate both clinical assessment and research on early irritability.