Psychometric properties of fatigue severity and fatigue impact scales in postpolio patients

We evaluate the reliability, validity, and responsiveness of the Fatigue Severity Scale (FSS) and the Fatigue Impact Scale (FIS) and to determine whether these scales are potentially applicable for measuring fatigue in postpolio patients (PPS). After the Turkish adaptation of FSS and FIS using a forward-backward procedure, the scales were administered to 48 PPS patients without additional health problems that may induce fatigue. Reliability studies were carried out by determination of intraclass correlation coefficient and internal consistency by the Cronbach-α coefficient. Validity was tested by within-scale analyses and analyses against the external criteria including convergent validity and discriminant validity. Correlations with the Notthingham Health Profile (NHP), fatigue, pain and cramp severity (visual analog scale), and manual muscle testing were performed. Sensitivity to changes was determined by standardized response mean values. All patients completed scales, suggesting their satisfactory acceptance. Reliability studies were satisfactory, with higher Cronbach-α values and intraclass correlation coefficients than 0.80. The FSS score was correlated moderately with visual analog scale-fatigue (r=0.41) and the NHP-energy dimension (r=0.29). All FIS scores except cognitive scores were moderately related to the NHP-social isolation score (r=0.40, 0.37, and 0.43 for FIS-physical, social, and total scores, respectively). There was also a significant correlation between the FIS-physical score and the NHP-energy score (r=0.31). On the basis of the standardized response mean values, response to treatment for these two questionnaires was satisfactory (P=0.00). The Turkish versions of FSS and FIS were reliable, sensitive to clinical changes, and also well accepted by patients with PPS. Although they had somewhat satisfactory convergent validity, the absence of strong correlations did not support the validity entirely.