Assessment of fatigue in primary Sjögren's syndrome: the Swedish version of the Profile of Fatigue

Abstract

To translate the disease-specific Profile of Fatigue (ProF) into Swedish and to evaluate the reliability and validity of the Swedish version. Forward and back translations were performed. Seventy patients with primary Sjögren's syndrome (PSS), 48 control persons, and two rheumatologists participated. Test-retest reliability, internal consistency, content, construct and discriminant validity were investigated. The translation was accepted without modifications. The test-retest reliability varied between moderate and good (weighted Kappa = 0.51-0.63). Internal consistency was high (Cronbach's alpha = 0.97). Construct validity was proved by significant correlations of the questionnaire items with the Visual Analogue Scale (VAS) for fatigue (r(s) = 0.55-0.70), and the Physical Function (PF) (r(s) = -0.20 to -0.41) and Vitality (VT) scales (r(s) = -0.60 to -0.77) of the MOS 36-Item Short-Form Health Survey (SF-36). Content validity was mainly judged as good. A significant difference between the scorings of the patients and the scorings of the control group was seen (mean difference 1.6, p<0.005). The Swedish version of the ProF is a relatively reliable and valid instrument for the measurement of fatigue in patients with PSS.