Validity and reliability of the Danish and Swedish versions of the Bristol Rheumatoid Arthritis Fatigue Questionnaires in patients with spondyloarthritis

Good 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.