Cross-cultural adaptation and validation of the Bangla version of the Psoriasis Disability Index

The Psoriasis Disability Index (PDI) is used for the quality-of-life assessment of psoriasis patients. However, a locally adapted Bangla version of the PDI (B-PDI) instrument is currently lacking in Bangladesh. To translate the instrument, adapt, and validate it among psoriatic patients of the country was the objective of the study.

Translation, adaptation, and back-to-back translation to Bangla were made from the original English PDI. The final Bangla instrument was applied among 83 psoriasis patients twice at 10 days intervals. The psychometric property of the instrument was evaluated. Item-level content-validity index (CVI) was used to check the content validity of the instrument. Convergent validity was tested by comparing the B-PDI with the validated Bangla version of Short Form 36(SF-36) and the Psoriasis Area Disability Index (PASI) score. Necessary testing was used to assess internal consistency and test-retest reliability.

The B-PDI was well-accepted by the patients. It showed good internal consistency (Cronbach's alpha = 0.76) and very high test-retest reliability (Pearson r = 0.92, p < 0.001). The scale demonstrated excellent content validity (Content Valid Index [CVI] = 1). The instrument had satisfactory convergent validity with four components of SF-36. Pearson correlation coefficient for physical, emotional, social, and pain domains of SF-36 was 0.663, 0.644, 0.808, and 0.862, respectively, and for PASI score was 0.812. Factor exploration using Principal Component Analysis revealed four factors reflecting working disabilities, social, and hygienic disabilities, lifestyle difficulties, and leisure-associated disabilities.

This study supports the reliability and validity of the B-PDI instrument for measuring health-related quality-of-life for Bangla-speaking psoriasis patients.