THE FACTOR STRUCTURE, DIAGNOSTIC VALUE AND DIFFERENTIAL VALIDITY OF FATIGUE SEVERITY SCALE (FSS) IN PATIENTS WITH MULTIPLE SCLEROSIS (MS)

Fatigue is a common symptom of Multiple Sclerosis (MS) for measurement of which، Fatigue Severity Scale (FSS) has many applications in these patients. Therefore، present study aimed at designing a psychometric research to assess the factor structure، diagnostic value and differential validity of the Persian version of FSS in patients with MS. This study was descriptive and validation type، in which 162 patients and 43 healthy individuals were selected by consecutive method and were matched in terms of demographic factors. Factor structure، diagnostic value and differential validity of this scale were examined. For this purpose، in addition to conducting FSS on subjects، they were further evaluated using the Short Form Health Survey (SF-36) and Depression، Anxiety and Stress Scale (DASS-21). Data were analyzed by factor analysis، discriminant analysis and independent t-test. FSS is a scale with one-factor structure. The findings from exploratory factor analysis (EFA) also confirmed the factor structure of the fatigue scale. Results of discriminant analysis showed that FSS could distinguish fatigue between two groups of healthy subjects and MS patients from each other. Its overall classification accuracy is equal to 74. 1%. Also، the mean of scores of all components related with quality of life and psychopathological symptoms in fatigued patients compared to non-fatigued patients was significantly greater with considering cut off point ≤ 4. Findings suggest that Persian version of FSS have acceptable screening performance in MS patients and can be used for patients in research situations and measures related with follow-up care.