Psychometric testing of the British English Workplace Activity Limitations Scale in four rheumatic and musculoskeletal conditions
Objectives: The aims were to validate a British English version of the Workplace Activity Limitations Scale (WALS) linguistically, then test this psychometrically in RA, axial spondyloarthritis (axSpA), OA and FM. Methods: The WALS was forward translated, reviewed by an expert panel, and cognitive debriefing interviews were conducted. Participants completed a postal questionnaire booklet. Construct (structural) validity was examined by fit to the Rasch measurement model. Concurrent validity included testing between the WALS and the Work Limitations Questionnaire-25 (WLQ-25). Two weeks later, participants were mailed a second questionnaire booklet for test-retest reliability. Results: Minor wording changes were made to the WALS, then 831 employed participants completed questionnaires: 267 men and 564 women; 53.5 (s.d. 8.9) years of age; with condition duration 7.7 (s.d. 8.0) years. The WALS satisfied Rasch model requirements, and a WALS Rasch transformation table was created. Concurrent validity was strong with the WLQ-25 (RA r s = 0.78; axSpA r s = 0.83; OA r s = 0.63; FM r s = 0.64). Internal consistency was consistent with group use (a = 0.80-0.87). Test-retest reliability was excellent, with intraclass correlation coefficient (2,1) at =0.90. Conclusion: A reliable, valid British English version of the WALS is now available for use in the UK.