Examining the validity of the multiple-sclerosis walking scale-12 with Rasch analysis: Results from an Italian study

Background: The Multiple Sclerosis Walking Scale (MSWS-12) has showed good psychometric properties in reports exploring its validity using Classical Test Theory methods. Findings from recent studies using Item Response Theory methods advance the idea that some aspects of the MSWS-12 does not fully comply with some requirements of sound measurement. Research question: The present study investigated whether the measurement properties of the Italian version of the MSWS-12 met the assumptions of the Rasch model. Methods: Sample consisted of 199 patients with a diagnosis of MS (50% female; Mean age (SD) = 48.15 (12.33)). Analyses were performed using both unidimensional and multidimensional Rasch modeling techniques. Results: Rating scale for items assessing need for support when walking, and ability to run, showed significant functioning problems. A revision of the rating scale improved the measurement properties of these items. Items assessing need for support showed signs of multidimensionality and differential item functioning when controlling for patients' disease course and EDSS score. Additionally, included items did not appear to cover the full range of impairment as observed in the sample. Significance: Emerging findings are consistent with those from previous studies in highlighting the need for a revision of the current content of the MSWS-12, and the inclusion of new items assessing impairment at the lower end of the disability continuum