Validity and reliability of the Danish and Swedish versions of the Bristol Rheumatoid Arthritis Fatigue questionnaires in patients with spondyloarthritis
ObjectiveTo investigate the validity, reliability, and interpretability of the Danish and Swedish versions of the Bristol Rheumatoid Arthritis Fatigue Multi-Dimensional Questionnaire (BRAF-MDQ) and Bristol Rheumatoid Arthritis Fatigue Numerical Rating Scales (BRAF-NRS V2) (BRAFs) in patients with spondyloarthritis (SpA).MethodThe BRAFs were tested for validity and reliability in an online survey. Participants were identified in the national rheumatology databases.ResultsIn Denmark, 234/435 participants (53.8%) completed the first survey (T1), of whom 125 (82.2%) also completed the second survey (T2) (mean ± sd age 59.6 ± 13 years, 52.6% women). In Sweden, 183/420 participants (43.6%) completed T1, of whom 171 (93.4%) also completed T2 (age 54.7 ± 13 years, 62.3% female). In both Denmark and Sweden, the content validity was supported for the BRAFs; regarding structural validity for BRAF-MDQ, explanatory factor analysis identified five factors; Cronbach’s α (internal consistency) was 0.94/0.95 for BRAF-MDQ and 0.79–0.93/0.76–0.94 for the four subscales; intraclass correlation coefficients (ICCs) were 0.96/0.93 for BRAF-MDQ and 0.84–0.93/0.86–0.90 for the subscales, and ICCs of the three BRAF-NRS scales were 0.70–0.90/0.71–0.89; and Construct validity: 80% of the hypotheses were fulfilled for the BRAFs.ConclusionsGood content validity, acceptable construct validity, good reliability, and low degree of measurement error were found for BRAF-MDQ and BRAF-NRS V2. BRAF-MDQ had acceptable structural validity, but five factors were identified, instead of four, suggesting caution in distinguishing dimensions of fatigue. The BRAFs are considered valid and reliable for measuring fatigue in Danish and Swedish patients with SpA
