Rasch analysis of the Multiple Sclerosis Impact Scale MSIS-29

Area of Science:

• Neurology
• Psychometrics
• Health Outcomes Research

Background:

• Multiple Sclerosis (MS) significantly impacts quality of life through physical and psychological impairments.
• The Multiple Sclerosis Impact Scale (MSIS-29) measures patient-reported HRQoL in MS.
• Previous psychometric evaluations of MSIS-29 used traditional methods, lacking detailed Rasch analysis.

Purpose of the Study:

• To conduct a comprehensive Rasch analysis of the MSIS-29.
• To evaluate the scale's internal validity, response format, item fit, targeting, internal consistency, and dimensionality.
• To assess the psychometric properties of the MSIS-29 physical (MSIS-29-PHYS) and psychological (MSIS-29-PSYCH) subscales.

Main Methods:

• Ninety-two individuals with definite MS were recruited from a tertiary hospital.
• Patients completed the MSIS-29 as part of a larger study.
• Rasch analysis was applied to evaluate the MSIS-29's psychometric properties.

Main Results:

• Rasch analysis supported the psychometric properties of both MSIS-29 subscales.
• The MSIS-29-PHYS response format was optimized to a 3-point scale.
• Both subscales demonstrated unidimensionality and good internal consistency, free from item bias for sex and age.
• Dimensionality testing advised against combining subscales into a total MSIS score.

Conclusions:

• Rasch analysis supports the use of the MSIS-29 physical and psychological subscales.
• The study does not support the use of a total MSIS-29 score.
• Further Rasch analysis in larger, diverse MS populations is recommended to confirm findings.