Evaluation of internal consistency and re-test reliability of Bath ankylosing spondylitis indices in a large cohort of adult and juvenile spondylitis patients in Taiwan

The Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), Bath Ankylosing Spondylitis Functional Index (BASFI), and Bath Ankylosing Spondylitis Global Score (BAS-G) have been recommended for evaluating function and disability in patients with ankylosing spondylitis (AS). The aim of this study was to develop a Chinese version of the BASDAI, BASFI, and BAS-G and assess their reliability and validity. The Chinese version was obtained after a translation and back-translation process. A total of 447 patients with adult and juvenile AS were assessed using these three instruments. Reliability was tested by internal consistency and test–retest reliability. Internal consistency of the instrument was given as Cronbach’s alpha. Test–retest reliability was assessed by intraclass correlation coefficient. To assess the sensitivity to change, 153 patients were included in an 8-week follow-up study. In our analysis, the reliability of these three instruments—the BASDAI, BASFI, and BAS-G—for a 24-h test–retest showed acceptable intraclass correlation coefficients (0.92–0.94). Our Chinese versions of the BASDAI, BASFI, and BAS-G also showed 0.87, 0.94, and 0.90, respectively, with Cronbach’s alpha coefficient, indicating good reliability. For sensitivity to change in 8-week follow-up, all three instruments showed 5.0 to 5.4% changes. Our Chinese versions of the BASDAI, BASFI, and BAS-G showed adequate reliability, validity, and responsiveness to clinical change. Thus, disease activity and functional status in Chinese-speaking patients with AS may be adequately evaluated with these versions of the original instruments.