Background: Measurement properties of the Weiss Functional Impairment Rating Scale-Parent Report Form (WFIRS-P), which assesses attention-deficit/hyperactivity disorder (ADHD)-related functional impairment in children/adolescents (6-17 years), were examined.
Methods: Data from seven randomized, controlled trials were pooled. Analyses were conducted in two random half-samples. WFIRS-P conceptual framework was evaluated using confirmatory factor analyses (CFA). Reliability was estimated using internal consistency (Cronbach's alpha) and test-retest reliability methods. Convergent validity was assessed using correlations between WFIRS-P domain scores and the ADHD-RS-IV and Clinical Global Impression-Severity (CGI-S) scales. Responsiveness was tested by comparing mean changes in WFIRS-P domain scores between responders and non-responders based on clinical criteria.
Results: CFA adequately confirmed the item-to-scale relationships defined in the WFIRS-P conceptual framework. Cronbach's alpha coefficient exceeded 0.7 for all domains and test-retest reliability exceeded 0.7 for all but Risky Activities. With few exceptions, WFIRS-P domains correlated significantly (p < 0.05) with ADHD-RS-IV Total, Inattention and Hyperactivity-Impulsivity scores and CGI-S at baseline and follow-up in both random half-samples. Mean changes in WFIRS-P domain scores differed significantly between responder and non-responder groups in the expected direction (p < 0.001).
Conclusions: Study results support the reliability, validity and responsiveness of the WFIRS-P. Findings were replicated between two random samples, further demonstrating the robustness of results.