Reliability, validity, and responsiveness of five at-work productivity measures in patients with rheumatoid arthritis or osteoarthritis.

OBJECTIVE: Arthritis often impacts a worker's ability to be productive while at work. However, the ideal approach to measuring arthritis-attributable at-work productivity loss remains unclear. Our objective was to evaluate the relative strengths and weaknesses of 5 measures aimed at quantifying health-related at-work productivity loss and to determine the best available instrument for this population.
METHODS: In a 12-month longitudinal design, the psychometric properties (reliability, validity, and responsiveness) of 5 self-reported measures of at-work productivity were compared in workers with either rheumatoid arthritis (RA) or osteoarthritis (OA). We tested the Workplace Activity Limitations Scale (WALS), 6-item Stanford Presenteeism Scale (SPS-6), Endicott Work Productivity Scale (EWPS), RA Work Instability Scale (WIS), and Work Limitations Questionnaire (WLQ).
RESULTS: Across all measures, participants (n = 250, 120 with RA and 130 with OA) consistently reported mild losses of at-work productivity. The Cronbach's alpha of the scales ranged from 0.71 (for SPS-6) to 0.94 (for EWPS), indicating some concerns over the internal consistency of the SPS-6. The RA WIS demonstrated the strongest construct validity (|r| = 0.54-0.74), whereas the WALS was most responsive to perceived changes in work ability. Despite its increasing popularity and potential application for costing analysis, the WLQ did not compare favorably with the other scales, possibly due to psychometric concerns with its physical demands subscale.
CONCLUSION: Measures revealed unique conceptualization of at-work disability, but no single scale emerged as clearly superior. However, current results slightly favor the WALS and RA WIS as superior instruments for measuring at-work productivity loss in workers with arthritis.