Longitudinal measurement invariance of the Multiple Sclerosis Walking Scale-12.

OBJECTIVE

One primary assumption underlying the unambiguous interpretation of change in Multiple Sclerosis Walking Scale-12 (MSWS-12) scores over time is longitudinal measurement invariance (i.e., Is the same construct being measured over time?). Such an assumption was tested in the present study over periods of 6 and 12 months in persons with relapsing-remitting multiple sclerosis (RRMS).

METHOD: Participants completed a battery of questionnaires that included the MSWS-12 at baseline (n=269) and 6-months (n=260) and 12-months (n=252) follow-up. The data were analyzed using confirmatory factor analysis and a series of nested model comparisons in Mplus 3.0.

RESULTS

The results indicated that the unidimensional measurement model and all of its parameters (e.g., factor loadings and item intercepts) were invariant over periods of 6 and 12 months.

CONCLUSION

We provide novel evidence that supports the unambiguous interpretation of scores from the MSWS-12 as a measure of change in walking impairment over time in a sample of persons with MS.