Performance of response scales of activity and functional measures of ankylosing spondylitis: numerical rating scale versus visual analog scale

The aim of this study was to compare the performance characteristics of two answer modalities for BASDAI and BASFI in patients with AS and to show validity and reliability of NRS in Turkish version. BASDAI and BASFI were simultaneously employed with a 10-cm VAS and an 11-point NRS. Internal consistency was assessed by using Cronbach’s alpha coefficients. Testing was performed on baseline and next day under standardized conditions. Construct validity was determined by association of these measures with ASDAS, DFI, global disease activity, pain scores, ASQOL, HAQ, and SF-36. We also tested the ability of NRS version of BASDAI and BASFI to detect changes. A total 114 patients with AS according to the modified New York criteria were included. There was a good agreement between the total scores of each instrument on day 0 (ICC values were 0.894–0.934). Scores of the both answering modality of each instrument were correlated with ASDAS-CRP, and the scores of DFI, patient global assessment of disease activity and patient-reported pain, ASQOL, HAQ. Response time for BASDAI and BASFI was significantly shorter in NRS answer modality (P < 0.001). Our patients found NRS modality more comprehensible and easier to understand (P < 0.001). Our results showed the validity of NRS version of BASDAI and BASFI and provided an evidence for using these questionnaires in 11-point NRS answer modality in Turkish AS patients.