Validation of the Fatigue Severity Scale in a Swedish burn population

Background : A burn injury is a complex trauma often followed by complications, one of them being fatigue. The objective of this study was to validate the Fatigue Severity Scale (FSS) in a Swedish burn cohort. Methods: A prospective study was performed at the Burn Center at Uppsala University Hospital, Sweden. All patients registered for follow-up 6 months after burn injury were asked to participate. Included patients completed questionnaires at 6- and 12-months postburn. Internal consistency (Cronbach’s alpha) and concurrent validity (Spearman´s rho) was calculated by comparing FSS with Brief Fatigue Inventory (BFI), the latter considered as “gold standard”. A linear regression analysis was used to establish the predictive validity. Convergent validity was evaluated through the correlation with other measurement tools covering fatigue, quality of life, depression/anxiety and daily activities. Results: Seventy included patients fulfilled both visits. FSS total scores demonstrated good internal consistency (Cronbachs alpha: 0.96 at both time points). A high concurrent validity was shown on both occasions (Spearman´s rho : 0.816 and 0.863 respectively). The linear regression analysis showed a relatively strong correlation, R ² = 0.66 at 6 months and 0.71 at 12 months which means that 66% of the BFI score is explained by the FSS at 6 months, and 71% at 12 months. A high statistically significant correlation (p<0.001) was seen between the two fatigue assessments and quality of life, depression/anxiety and daily activities showing that the more severe the fatigue, the more severe the depressive and anxiety symptoms, and the greater the impairment of quality of life and the performance of daily activities. No important floor- or ceiling effects were observed in either of the fatigue assessments. Conclusion: The result indicates that the two fatigue scales correspond and measure similar aspects of fatigue, and that the FSS is a valid and reliable measurement of fatigue in adult burn patients in Sweden. However, future research is needed especially to establish the content validity of the FSS within the Swedish cohort of burn patients.