Adaptation and crosscultural validation of the Foot Impact Scale for Rheumatoid Arthritis using Rasch analysis.

Area of Science:

• Rheumatology
• Psychometrics
• Health Outcomes Measurement

Background:

• Rheumatoid Arthritis (RA) significantly impacts foot health and daily activities.
• Validated instruments are crucial for assessing RA-related foot problems across different cultures.
• The Foot Impact Scale for Rheumatoid Arthritis (FIS-RA) requires cross-cultural adaptation and validation.

Purpose of the Study:

• To adapt and cross-culturally validate the FIS-RA for German, Hungarian, and Dutch language versions.
• To assess the psychometric properties of the FIS-RA using Rasch analysis.
• To ensure the FIS-RA is suitable for individual patient assessment and group-level research.

Main Methods:

• Translation of the FIS-RA into German, Hungarian, and Dutch.
• Administration to 653 rheumatoid arthritis patients.
• Rasch analysis applied to impairment/footwear and activity limitation/participation restriction subscales, including testing for fit, unidimensionality, differential item function (DIF), and local response dependency.
• Item deletion, subtest analysis, and item splitting were used to meet Rasch model assumptions.

Main Results:

• Initial Rasch analysis showed poor fit for most language versions and pooled data, indicating multidimensionality, misfitting items, local dependency, and DIF.
• Adjustments including item deletion and splitting successfully achieved satisfactory fit to the Rasch model for all language versions.
• Pooled data met Rasch model assumptions for cross-cultural validity after adjustments for language DIF.

Conclusions:

• The adapted FIS-RA is successfully translated and cross-culturally validated for use in four European languages.
• The two subscales of the FIS-RA demonstrate suitability for both individual patient assessment and group-level research.
• This validated instrument enhances the ability to measure foot impact in rheumatoid arthritis patients across diverse linguistic backgrounds.