Adaptation and validation of the Ankylosing Spondylitis Work Instability Scale (AS-WIS) for use in Turkey

The Ankylosing Spondylitis Work Instability Scale (AS-WIS) is a recently developed 20-item measure to assess work instability in AS. This study aimed to adapt the AS-WIS to Turkish and to test its reliability and validity. After the translation process, 132 AS patients were assessed by the AS-WIS, Bath AS Disease Activity Index, Bath AS Functional Index and the AS Quality of Life Questionnaire. Reliability was tested by internal consistency, person separation index (PSI) and intra-class correlation coefficient (ICC); internal construct validity by Rasch analysis; external construct validity by associations with comparator scales and cross-cultural validity by comparison with the original UK data. Reliability of the Turkish AS-WIS was good with Cronbach's α and PSI of 0.88 and test-retest ICC of 0.91. Data showed good fit to Rasch model [mean item fit: -0.477 (SD 1.047), Chi-square interaction: 60.9 (df = 40, p = 0.018)]. There was no differential item functioning by age, gender, disease duration or work type. The scale was strictly unidimensional. 51 % of the patients were at moderate risk, and 9 % were at high risk of having to give up their work. External construct validity was confirmed by expected correlations with comparator scales, and a clear gradient of disease activity and functional status across increasing levels of risk. Cross-cultural validity showed some differences in item locations, but this cancelled out at the test level. Turkish version of the AS-WIS is reliable, valid and available for use in routine clinical setting to identify patients who are at risk of having to give up their current job.