Adaptation and crosscultural validation of the foot impact scale for rheumatoid arthritis using Rasch analysis

Objective. To adapt and crossculturally validate the Foot Impact Scale for Rheumatoid Arthritis (FIS-RA) using Rasch analysis. Methods. The FIS-RA was translated from English to German, Hungarian, and Dutch target languages and administered to 653 rheumatoid arthritis patients. Rasch analysis was undertaken on the impairment/footwear (FIS-RA IF) and activity limitation/participation restriction subscales for each language version separately and for pooled data. Overall fit to the Rasch model, item and person fit, unidimensionality, differential item function (DIF), and local response dependency were tested. To meet Rasch model assumptions, item deletion, subtests analysis, and item-splitting strategies were adopted. Results. With the exception of the Hungarian FIS-RA IF subscale, preliminary fit to the Rasch model was unsuccessful for all target languages individually and for pooled data. Multidimensionality, misfitting items, local dependency, and DIF by age, sex, disease duration, and language were observed. With adjustment, fit to the Rasch model was satisfactorily achieved for all language versions. For the pooled data, the Rasch model assumptions for crosscultural validity were met following item deletion, subtest analysis, and item splitting for language DIF. Conclusion. With adaptations, the FIS-RA was successfully translated and crossculturally validated for use in 4 European languages. The 2 subscales can be used at the individual level for patient assessment and at the group level for research purposes.