Cross-cultural adaptation and validation of the Manchester Foot Pain and Disability Index into Spanish

Abstract

Purpose The Manchester Foot Pain and Disability Index (MFPDI) is a self-assessment 19-item questionnaire developed in the UK to measure foot pain and disability. This study aimed at conducting cross-cultural adaptation and validation of the MFPDI for use in Spain. Methods Principles of good practice for the translation and cultural adaptation process for patient-reported outcomes measures were followed in the MFPDI adaptation into Spanish. The cross-cultural validation involved Rasch analysis of pooled data sets from Spain and the UK. Results Spanish data set comprised 338 patients, five used in the adaptation phase and 333 in the cross-cultural validation phase, mean age (SD) = 55.2 (16.7) and 248 (74.5 %) were female. A UK data set (n = 682) added in the cross-cultural validation phase; mean age (SD) = 51.6 (15.2 %) and 416 (61.0 %) were female. A preliminary analysis of the 17-item MFPDI revealed significant local dependency of items causing significant deviation from the Rasch model. Grouping all items into testlets and re-analysing the MFPDI as a 3-testlet scale resulted in an adequate fit to the Rasch model, v2 (df) = 15.945 (12), p = 0.194, excellent reliability and unidimensionality. Lack of cross-cultural invariance was evident on the functional and personal appearance testlets. Splitting the affected testlets discounted the cross-cultural bias and satisfied requirements of the Rasch model. Subsequently, the MFPDI was calibrated into interval-level scales, fully adjusted to allow parametric analyses and cross-cultural data comparisons when required. Conclusions Rasch analysis has confirmed that the MFPDI is a robust 3-subscale measure of foot pain, function and appearance in both its English and Spanish versions.