Development of a short version of MSQOL-54 using factor analysis and item response theory

Background: The Multiple Sclerosis Quality of Life-54 (MSQOL-54, 52 items grouped in 12 subscales plus two single items) is the most used MS specific health related quality of life inventory. Objective: To develop a shortened version of the MSQOL-54. Methods: MSQOL-54 dimensionality and metric properties were investigated by confirmatory factor analysis (CFA) and Rasch modelling (Partial Credit Model, PCM) on MSQOL-54s completed by 473 MS patients. Their mean age was 41 years, 65% were women, and median Expanded Disability Status Scale (EDSS) score was 2.0 (range 0-9.5). Differential item functioning (DIF) was evaluated for gender, age and EDSS. Dimensionality of the resulting short version was assessed by exploratory factor analysis (EFA) and CFA. Cognitive debriefing of the short instrument (vs. the original) was then performed on 12 MS patients. Results: CFA of MSQOL-54 subscales showed that the data fitted the overall model well. Two subscales (Role Limitations-Physical, Role Limitations-Emotional) did not fit the PCM, and were removed; two other subscales (Health Perceptions, Social Function) did not fit the model, but were retained as single items. Sexual Satisfaction (single-item subscale) was also removed. The resulting MSQOL-29 consisted of 25 items grouped in 7 subscales, plus 4 single items. PCM fit statistics were within the acceptability range for all MSQOL-29 items except one which had significant DIF by age. EFA and CFA indicated adequate fit to the original two-factor (Physical and Mental Health Composites) hypothesis. Cognitive debriefing confirmed that MSQOL-29 was acceptable and had lost no key items. Conclusions: The proposed MSQOL-29 is 50% shorter than MSQOL-54, yet preserves key quality of life dimensions. Prospective validation on a large, independent MS patient sample is ongoing.