Background To date there is an unmet need for an instrument assessing presenteeism and absenteeism in both the work and home environment in psoriatic arthritis (PsA). The novel arthritis-specific Work Productivity Survey (WPS) was developed to estimate productivity limitations associated with arthritis on paid jobs outside the home, on unpaid work within the home, and on social activities during the preceding month.1 The WPS was validated in rheumatoid arthritis.1
Objectives To assess the discriminant validity, responsiveness and reliability of the WPS in adult-onset PsA.
Methods Psychometric properties were assessed using data from the RAPID-PsA trial (NCT01087788) investigating certolizumab pegol (CZP) efficacy and safety in PsA.2 The WPS is comprised of 9 questions: employment status, workplace productivity (absenteeism, presenteeism) and household productivity (days missed of household work, days with reduced productivity, days missed of family/social/leisure activities, days with outside help, level of arthritis interference on home productivity). WPS was completed at BL and every 4 weeks (wks) until Wk24. The validity was evaluated via known-groups approach: mean WPS scores at BL were compared between patients (pts) with a worse health state (ie. with a higher disease activity, or a worse health-related quality-of-life level or a lower physical functioning) vs pts with a better health state. Groups were defined by the 1st and 3rd quartiles cut-off of the pts’ scores to DAS28(CRP), HAQ-DI, SF-36 and PsAQoL. Sensitivity analyses were performed using the median-cut of the scores. The WPS responsiveness and reliability was assessed by comparing WPS mean changes at Wk12 in ACR20 or HAQ-DI MCID 0.3 responders vs non-responders. All comparisons were conducted on the observed cases in the Randomized Set, regardless of the randomization group, using a non-parametric bootstrap-t method.
Results Results confirmed the discriminant validity of WPS in PsA. Compared with pts with a better health state, pts with a worse health state had on average significantly 2 to 6 times more household work days lost, more days with household productivity reduced by ≥50%, more days missed of family/social/leisure activities, more days with outside help hired and a significantly higher interference of arthritis per month. Among employed pts, those with a worse health state had significantly 2 to 4 times more work days lost and more work days with productivity reduced by ≥50%, and a statistically higher interference of arthritis on work productivity vs pts with a better health state. WPS was also responsive to ACR20 or HAQ-DI MCID clinical changes at Wk12. Responders had significantly larger improvements at Wk12 in WPS scores vs non-responders. The effect sizes for changes in productivity in ACR20 or HAQ-DI MCID responders were moderate (0.5<SRM<0.8) or small (in WPS Q2, Q7).
Conclusions These analyses demonstrate that WPS is a valid, responsive and reliable instrument for the measurement of productivity within and outside the home in an adult-onset PsA population.
Osterhaus J. Arth Res Ther 2009;11:R73;
Mease P. Ann Rheum Dis 2012;71(Suppl3):150
Acknowledgements The authors acknowledge Costello Medical Consulting for writing and editorial assistance which was funded by UCB Pharma.
Disclosure of Interest J. Osterhaus Consultant for: Advanced BioHealing, InterMune, Pfizer, Theravance and UCB Pharma, O. Purcaru Employee of: UCB Pharma