Performance of the SF-36, SF-12, and RAND-36 summary scales in a multiple sclerosis population

BACKGROUND. Multiple sclerosis (MS) patients accumulate both physical and m ental health problems along with disease progression. Valid and sensitive o utcome measures are important to measure disease effects and the effect of treatment. OBJECTIVE. The objective of this study was to test the performance of the p hysical and mental summary scales of SF-36, SF-12, and RAND-36. METHODS. The scales were evaluated by comparing the scores of a cohort of 1 94 MS patients with general population data and using the Expanded Disabili ty Status Scale (EDSS) and the Incapacity Status Scale-mental as criterion variables for physical functioning and mental health. RESULTS. All 3 physical summary scales were markedly reduced and correlated highly with the EDSS. The SF-36 mental summary score was only slightly red uced among MS patients (0.2 SD) compared with the general population, despi te significantly reduced scores on all 4 health scales being most related t o mental health and despite a high prevalence of mental health problems. Th is results from the poor physical functioning (mean scale score, 2.3 SD bel ow the general population) and the orthogonal factor rotation used to deriv e independent measures of physical and mental health. Similar results were found for the SF-12. The nonorthogonal RAND-36 physical and mental summary scores were both markedly reduced. This is more compatible with the disease progression in MS and the results of the other measures of physical and me ntal health used in the study. CONCLUSIONS. The SF-36 and SF-12 mental health summary scales appear to ove restimate mental health in people with MS.