Background Inflammatory arthritis (IA) and osteoarthritis (OA) often impact on the worker's performance whilst at work due to ill health (i.e. presenteeism). A number of global measures have been developed to assess presenteeism in clinical studies. However, limited information is available on the correlation between these measures and the construct validity of these measures.
Objectives To i) determine the correlation between four global measures of presenteeism and ii) to evaluate the construct validity of these measures.
Methods The main aim of this international observational study (7 countries in Europe and Canada), recruiting patients with IA (RA, PsA or AS) or OA in paid employment, was to investigate content and construct validity of global presenteeism measures. Patients completed 4 global measures (Work Productivity Scale – Arthritis (WPS-A), Work Productivity and Activity Impairment Questionnaire (WPAI), Work Ability Index (WAI), and both the Quality and Quantity scales of the QQ questionnaire) (see table legend for descriptions individual scales). Spearman correlations were applied to test the correlation between individual presenteeism scales and to test construct validity with the 11-item Workplace Activity Limitation presenteeism Scale (WALS) and several health related patient reported outcome measures. Interpretation of correlation coefficients: (very) weak (rrange=0.0–0.39), moderate (rrange=0.40–0.59) to strong (rrange=0.60–1.0).
Results 468 patients with a median disease duration of 10 [IQR 5–18] yrs were included; 62% were female. Median [IQR] presenteeism scores were, respectively: 2 [0–5] for WPS-A, 3 [1–5] for WPAI, 8 [6–9] for WAI, 81 [49–100] QQ-total, with WAI and QQ having reversed scales (Legend table). Correlations between the 4 global measures were moderate to strong, ranging from -0.49 for the correlation between WPS-RA and QQ-Quality to 0.83 between WPAI and WPS-RA. The multi-item presenteeism scale WALS, measuring difficulty at work, strongly correlated with both WPAI (r=0.65, p<0.05) and WPS-RA (r=0.64, p<0.05), both measures capturing the affect and interference of arthritis on work productivity. Moderate correlations were achieved between all six global presenteeism measures and health outcomes (rrange irrespective direction: |rpresenteeism-VAS Well-being| =0.36 to 0.54; |rpresenteeism-EQ-5D| =0.37 to 0.54; and |rpresenteeism-HAQ| =0.40 to 0.58).
Conclusions Global measures of presenteeism show good to moderate construct validity, with the WPAI and WPS-IA/OA showing slightly better construct validity compared to the WAI and QQ. The information obtained in this study will further inform research on instrument use for a standardized approach to estimate presenteeism in future clinical studies.
Acknowledgements Funding: EULAR, AbbVie, BMS
Disclosure of Interest None declared