Investigating the Psychometric Properties of the Persian Version of the Revised Illness Perception Questionnaire in a Sample of Patients With Multiple Sclerosis.

Introduction: Illness perception significantly influences treatment adherence and quality of life among patients with multiple sclerosis (MS). Despite the widespread use of the Revised Illness Perception Questionnaire (IPQ-R) in different languages, a validated Persian version tailored for MS patients was lacking.

Methods: A cross-sectional study was conducted with 400 Persian-speaking MS patients recruited from the MS Society of Iran between December 2023 and April 2024. The IPQ-R was translated and culturally adapted through standard forward-backward translation procedures. Validity was assessed through face, content, and construct validity (using both confirmatory factor analysis [CFA] and exploratory factor analysis [EFA]). Reliability was evaluated using Cronbach's alpha and composite reliability (CR).

Results: The Persian IPQ-R showed strong face and content validity, with all items achieving acceptable content validity ratio (CVR) and content validity index (CVI) scores. CFA supported the original seven-factor model (χ/df = 1.048, CFI = 0.998, RMSEA = 0.011). EFA of the cause subscale revealed four interpretable dimensions explaining 75.6% of variance. Most subscales demonstrated excellent internal consistency (α = 0.839-0.962), whereas the identity subscale showed lower reliability (α = 0.590). Convergent and discriminant validity were confirmed through average variance extracted (AVE) and Heterotrait-Monotrait (HTMT) indices.

Conclusion: This study revealed that the Persian version of the IPQ-R is a reliable and valid instrument for assessing illness perceptions in Iranian MS patients. It may serve as a valuable tool in clinical and research settings to evaluate patient beliefs and guide personalized care strategies.