Validity and reliability of the Finnish version of the Multiple Sclerosis Impact Scale‐29

Background The Multiple Sclerosis Impact Scale‐29 (MSIS‐29) has been increasingly used to evaluate the self‐perceived impact of multiple sclerosis (MS) on a patient. Objectives The aim of this study was to evaluate the psychometric properties of the Finnish version of MSIS‐29 in patients with MS. Methods A total of 553 patients with MS completed the MSIS‐29 and self‐administered questionnaires capturing information on demographics, disease characteristics and severity, perceived quality of life (EuroQol 5D‐3L instrument), and fatigue (Fatigue Severity Scale). Results The data quality for MSIS‐29 was excellent, with 99.5% computable scores for the MSIS‐29 physical scale and 99.3% for the MSIS‐29 psychological scale. Floor and ceiling effects were minimal. Excellent Cronbach's alpha values of 0.97 and 0.90 were seen for MSIS‐29 physical and psychological subscales, respectively. The physical subscale showed highest correlations with measures of physical functioning, such as disease severity and the mobility domain of the quality of life. Similarly, the psychological subscale showed highest correlations with self‐reported fatigue and the anxiety/depression domains of the quality of life. MSIS‐29 physical scores related strongly to disease severity, whereas the MSIS‐29 psychological scores increased in mild disease but declined in more severe disease forms. Conclusion The Finnish version of MSIS‐29 has satisfactory psychometric properties. Consistent with the previous recommendations, the use of two MSIS‐29 subscale scores instead of a total score was supported. The purpose of this study was to evaluate the psychometric properties of the Finnish version of MSIS‐29 in terms of data quality, scaling assumptions, acceptability, validity, and reliability in a large sample of MS patients including all clinical phenotypes, and with a wide range of disability. Additionally, the dimensional structure of MSIS‐29 was evaluated.