Multiple Sclerosis Impact Scale (MSIS-29): reliability and validity in hospital based samples

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Abstract
Background and aim: The psychometric properties of rating scales are sample dependent and need evaluations in different samples. The Multiple Sclerosis Impact Scale (MSIS-29), a new patient based rating scale for multiple sclerosis (MS) was predominantly developed from a community based sample derived from the MS Society. A number of important patient characteristics of this sample remain unknown. The aim of the study was to evaluate five psychometric properties of the MSIS-29 in three hospital based samples: people admitted for rehabilitation, people admitted for intravenous corticosteroid treatment for MS relapses, and people with primary progressive MS. Methods: People with MS were recruited from the three clinical settings. They completed several health measures. MSIS-29 data were evaluated for data quality, scaling assumptions, acceptability, reliability and validity, and compared with those from a previously reported community based study. Results: A total of 233 people (rehabilitation =53; corticosteroids =76; primary progressive =104) completed questionnaires. In all samples, missing data were low (≤2.2%), scaling assumptions were satisfied, and reliability was high (≥0.91). Correlations between the MSIS-29 and other scales were consistent with a priori hypotheses. Findings were consistent with those from the community samples. Conclusions: The psychometric properties of the MSIS-29 are consistent across three hospital based samples, and similar to those in the community samples. These findings further support its use as an outcome measure in different clinical settings.