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Background Self-efficacy refers to people’s beliefs in their ability to perform relevant activities to achieve personal goals. In people with multiple sclerosis (PwMS), self-efficacy has been shown to significantly impact health-related behaviour. So far, a validated German language self-efficacy scale for PwMS is missing. Therefore, the aims his study were to translate the Unidimensional Self-Efficacy Scale for Multiple Sclerosis (USE-MS) into German, establish face and content validity and cultural adaption of the German version for PwMS in Austria. Further aims were to validate the German USE-MS (USE-MS-G) in PwMS using Rasch analysis. Methods Formal permission to translate and validate the USE-MS was received from the scale developers. Following guidelines for translation and validation of questionnaires and applying Bandura’s concept of self-efficacy, the USE-MS was forward-backward translated, and content and face validity established. Cultural adaption for Austria was performed using cognitive interviews of 30 PwMS. The validation by Rasch analysis, of the final USE-MS-G involved 309 PwMS with minimal to severe disability using scales for resilience, general self-efficacy, anxiety and depression, MS fatigue and health-related quality of life. Re-test was conducted within 14–21 days after the initial test. Data were also pooled with an historic English dataset. Results Using a bi-factor solution, excellent external and construct validity, internal consistency, person separation reliability, test-retest reliability and fit to the Rasch model was demonstrated. The USE-MS-G was shown to be unidimensional, well-targeted and free from differential item functioning. Pooling of the English and German datasets confirmed equivalence of the two language versions. Conclusion The USE-MS-G is a robust, valid and reliable scale to assess self-efficacy in PwMS. Rasch model fit given, an interval scale transformation table is available for clinical settings and research. Trial registration: ISRCTN Registry; ISRCTN14843579; prospectively registered on 02. 01. 2019; http://www.isrctn.com/ISRCTN14843579 |
