Validity of the Marshall Sitting Questionnaire in Persons with Multiple Sclerosis

Background: The Marshall Sitting Questionnaire (MSQ) has been validated based on accelerometry and applied for measuring sedentary behavior (SB) in the general population. No studies have examined its validity in persons with multiple sclerosis (MS), which is important considering recent emphasis on SB in this population. Objectives: 1) To examine the validity of the MSQ based on accelerometry-derived SB estimates in persons with MS and, 2) to develop a prediction model to improve the accuracy of the MSQ in persons with MS. Methods: Participants (n=63) completed the MSQ and wore an accelerometer on the hip for a 7-day period. SB estimates were computed as min/day for both the MSQ and accelerometer. Associations between the two measurement methods were examined using the Pearson correlation. A Bland-Altman plot was used to assess agreement and measurement bias of the MSQ in relation to accelerometry. A linear prediction model was developed to improve the accuracy of the MSQ estimates using a selection of predictor variables routinely collected in MS research. Results: The correlation between MSQ and accelerometer SB estimates was statistically significant but of small magnitude (r = 0.34, p < 0.01). The Bland-Altman plot indicated that the MSQ overestimated SB (mean bias: 80.54 min/day, 95% limits of agreement: -410.5 to 571.5 min/day). The prediction model improved the MSQ estimates by 39% and virtually eliminated measurement bias (mean bias: -0.21 min/day; 95% limits of agreement: -109.8 to 109.4 min/day). Conclusions: The results indicate preliminary evidence for the validity of the MSQ in persons with MS, and support the application of an alternative prediction model to improve the accuracy of the MSQ estimates.