Evaluating Differential Item Functioning in EQ-5D-5L in Acute Ischemic Stroke: Evidence From the ACT Trial

BACKGROUND: Health-related quality of life is a key secondary end point in stroke trials. Differential item functioning (DIF) occurs when individuals with the same underlying health-related quality of life interpret and respond differently to questionnaire items, potentially biasing treatment comparisons. This study evaluates DIF in the patient-reported 5-level EuroQOL questionnaire among patients with acute ischemic stroke across age, sex, and treatment groups. METHODS: Data were from the AcT trial (Alteplase Compared to Tenecteplase), a registry-based randomized comparison of alteplase and tenecteplase conducted at 22 stroke centers across Canada (December 2019-January 2022). Patients with acute ischemic stroke presenting within 4.5 hours of symptom onset and eligible for thrombolysis completed the 5-level EuroQOL questionnaire at 90 days poststroke. DIF was assessed using multigroup graded response models with the Wald-based sweep procedure, which accounts for between-group differences in latent trait distributions. We quantified effect sizes using signed weighted area between curves (sWABC); |sWABC| <0.10=negligible. RESULTS: =0.379) showed evidence of DIF. Four items flagged for age-related DIF: self-care, usual activities, pain/discomfort, and anxiety/depression. However, only self-care (sWABC=-0.46) and usual activities (sWABC=-0.34) showed moderate effects, while pain/discomfort (sWABC=-0.002) and anxiety/depression (sWABC=0.09) were negligible. Importantly, factor scores from models with and without DIF adjustment correlated (correlation coefficient=0.98). CONCLUSIONS: The 5-level EuroQOL questionnaire appears to function equivalently across sex and treatment groups in this stroke population. Age-related DIF, though statistically detectable in physical functioning items, had little practical consequence for individual scores, supporting the instrument's use for health-related quality of life comparisons in stroke trials. REGISTRATION: URL: https://www.clinicaltrials.gov; Unique identifier: NCT03889249.