Purpose: We developed the Arm Function in Multiple Sclerosis Questionnaire (AMSQ) to measure arm and hand function in MS, based on existing scales. We aimed at developing a unidimensional scale containing enough items to be used as an itembank. In this study, we investigated reliability and differential item functioning of the Dutch version.
Method: Patients were recruited from two MS Centers and a Dutch website for MS patients. We performed item factor analysis on the polychoric correlation matrix, using multiple fit-indices to investigate model fit. The graded response model, an item response theory model, was used to investigate item goodness-of-fit, reliability of the estimated trait levels (θ), differential item functioning, and total information. Differential item functioning was investigated for type of MS, gender, administration version, and test length.
Results: Factor analysis results suggested one factor. All items showed p-values of the item goodness-of-fit statistic above 0.0016. The reliability was 0.95, and no items showed differential item functioning on any of the investigated variables.
Conclusion: AMSQ is a unidimensional 31-item questionnaire for measuring arm function in MS. Because of a well fit in a graded response model, it is suitable for further development as a computer adaptive test. Implications for Rehabilitation A new questionnaire for arm and hand function recommended in people with multiple sclerosis (AMSQ). Scale characteristics make the questionnaire suitable for use in clinical practice and research. Good reliability. Further development as a computer adaptive test to reduce burden of (repetitive) testing in patients is feasible.
Keywords: Activity limitations; Arm Function in Multiple Sclerosis Questionnaire; differential item functioning; graded response model; item fit; item response model; multiple sclerosis; psychometrics.