The Multiple Sclerosis-Fatigue Self– Efficacy (MS-FSE) scale: initial validation

OBJECTIVE To examine the validity and sensitivity to change of the Multiple Sclerosis-Fatigue Self-Efficacy scale. DESIGN A validation study nested within a randomized controlled trial. SETTING Community setting. PARTICIPANTS Adults with a clinically definite diagnosis of multiple sclerosis and significant fatigue taking part in a randomized controlled trial evaluating a group-based fatigue management programme (FACETS) for people with multiple sclerosis (N=164). MAIN MEASURES The 9-item Multiple Sclerosis-Fatigue Self-Efficacy scale was completed at baseline, 1-, 4- and 12 months post intervention. Validity, internal consistency and sensitivity to change were examined using classical test theory and Rasch analysis. RESULTS Item 3 was unanswered by 6% of respondents as they did not know any other people with multiple sclerosis; remaining analyses were carried out with this item deleted. All response choices were utilised, no floor or ceiling effects were evident and there were few missing responses. Cronbach's alphas were high (baseline, 0.89; follow-up 1, 0.93; follow-up 2, 0.94; follow-up 3, 0.90). The Multiple Sclerosis-Fatigue Self-Efficacy scale (8-item) demonstrated good sensitivity to change following attendance of the FACETS programme (within participant effect sizes 0.66 and 0.69 and 0.54 at 1, 4, and 12 months follow-up). Principal Components Analysis yielded one component. In the Rasch analysis two items with disordered thresholds were rescored. Item 8 displayed differential item functioning by disability and was combined into a testlet with item 4, resulting in a unidimensional scale. The sample was well targeted to the scale. CONCLUSION At a scale level the Multiple Sclerosis-Fatigue Self-Efficacy scale is internally valid and has good sensitivity to change.