Validation of the Arabic Version of the Multiple Sclerosis Impact Scale (MSIS-29): a Rasch Analysis Study.

Background: Multiple sclerosis (MS) is a potentially disabling disease of the brain and spinal cord. This cross-sectional study aimed to validate the Arabic version of the Multiple Sclerosis Impact Scale-29 (MSIS-29) using Rasch analysis to assess quality of life in Jordanian MS patients.

Method: Rasch analysis was conducted to evaluate the suitability of the model for the present study. Model fit was assessed by computing item/person separation reliability, infit and outfit mean square (MSQ) values, Cronbach's alpha, and the Akaike Information Criterion.

Results: A total of 301 MS patients were enrolled in the study. Significant likelihood ratios for all three scales (MSIS-29-PHYSICAL, MSIS-29-PSYCHOLOGICAL, and MSIS-29-TOTAL) supported the use of a partial credit Rasch model. An issue with disordered thresholds was resolved by collapsing adjacent response categories. Item reliability scores for MSIS-29-PHYS and MSIS-29-PSYCH were 0.95 and 0.89, respectively, while person reliability scores were 0.92 and 0.84, respectively. Infit and outfit MSQ were within the acceptable range for all items on the MSIS-29-PSYCH scale. However, for the MSIS-29-PHYS scale, item MSIS-29_17 exceeded the acceptable range in both infit (1.93) and outfit (1.82) MSQs, and item MSIS-29_20 exceeded the acceptable range in infit (1.81). The Wright map also indicated that most items were considered relatively easy by the respondents, exhibiting various difficulty levels on the latent scale.

Conclusion: The Arabic version of the MSIS-29 is a valid and reliable tool for evaluating quality of life in Jordanian MS patients.