Psychometric validation of the psoriasis disability index questionnaire (Translated Bengali Version): A cross-sectional study

Introduction: The Psoriasis Disability Index (PDI) is a pre-validated, self-administered questionnaire assessing quality of life in adults suffering from psoriasis. The English version contains 15 items measuring five components - activities, work/school performance, personal, leisure, and treatment. Purpose: We aimed to translate the PDI into Bengali and examine its psychometric properties. Methods: The PDI-Bengali version (PDI-B) was produced by standardized forward-backward translations. A cross-sectional study was conducted to gather responses by consecutive sampling. Reliability was tested using internal consistency and test-retest reliability analyses, concurrent validity by comparing with Psoriasis Area and Severity Index (PASI) and Dermatological Life Quality Index scores, while construct validity by exploratory factor analysis (n= 83) using principal component analysis (varimax rotation). Subsequently, confirmatory factor analysis (CFA; n = 85) was performed to verify the a priori scales by the goodness of fit model. Results: The internal consistency (Cronbach's alpha) and the intra-class correlation coefficients were 0.877 and 0.882, respectively. Acceptable values of internal consistency, test-retest reliability, and concurrent validity were found. All the items loaded above the pre-specified value of 0.4. Factor analyses using Varimax identified three components (social activities, concern, and personal activities) explaining 56.8% of the variation. The Kaiser-Meyer-Olkin was 0.836 and Bartlett's test of sphericity was P < 0.001. The goodness of fit of CFA model was excellent. Conclusion: The PDI-B, consisting of 15 items and framed within three components, is a valid and reliable questionnaire, but measured different dimensions from the English version.