Discriminant validity, responsiveness and reliability of the rheumatoid arthritis-specific Work Productivity Survey (WPS-RA)

Abstract

Introduction The rheumatoid arthritis-specific Work Productivity Survey (WPS-RA) measures the impact of rheumatoid arthritis (RA) and treatment on patient productivity within and outside the home. It contains nine questions addressing employment status, productivity within and outside the home, and daily activities. The objective of this paper was to evaluate the discriminant validity, responsiveness, and reliability of the WPS-RA in patients with active RA. Methods Two hundred twenty subjects (mean age was 53.8 years, 83.6% were female, mean disease duration was 9.54 years, mean number of disease-modifying anti-rheumatic drugs failed was 2, and 38.6% were employed outside the home) in a phase III, 24-week, double-blind, placebo-controlled trial completed the WPS-RA at baseline and every 4 weeks until withdrawal/study completion. Validity was evaluated via known groups using baseline data (first and third quartiles of subjects' Health Assessment Questionnaire – Disability Index [HAQ-DI] scores and Short Form-36 health survey [SF-36] scores). To evaluate responsiveness, mean changes in WPS-RA at week 24 were compared between American College of Rheumatology 20% improvement criteria (ACR20) (or HAQ-DI) responders and non-responders. Standardized response mean (SRM) was also used to quantify responsiveness. All group comparisons were conducted using a non-parametric bootstrap-t method. Results Subjects with lower HAQ-DI or SF-36 scores generally had statistically greater RA-associated losses in productivity within and outside the home compared with subjects with higher scores (25 of 32 evaluations were statistically significant). Smallest differences between groupswere seen in work absenteeism and days with outside help. At week 24, ACR20 and HAQ-DI responders reported large improvements in productivity within and outside the home; non-responders reported mainly a worsening in productivity ( P ≤ 0.05). Effect size for productivity changes in ACR20 or HAQ-DI responders was moderate to large for six out of eight items (SRM = 0.48 to 1.12). The effect size was small for work absenteeism and days with outside help. (SRM = 0.4 and 0.24, respectively). In non-responders, the magnitude of change was negligible (SRM < 0.1) or small (SRM < 0.3). Conclusions The WPS-RA has demonstrated properties of discriminative validity, reliability, and responsiveness for the measurement of productivity within and outside the home in subjects with active RA.

Assessment of physical function and participation in chronic pain clinical trials: IMMPACT/OMERACT recommendations

“…Large survey or population health data can separate some of these diverse factors, but it is challenging to determine what should be included as outcome measures in a clinical trial. Several validated instruments are available that assess changes in the activities that are important to patients, for example, the Work Productivity Survey (WPS, the only questionnaire to query family, social, and leisure activities as well as work within the home) 141 , the Work Limitations Questionnaire (WLQ) 9,112,113 , and the Workplace Activity Limitations Scale (WALS). 17,67,69 Such outcome measures should be considered for inclusion in clinical trials where there is an expectation that work will be affected by the treatment.…”

Certolizumab Pegol

“…29 Over one year in RAPID 1, patients treated with certolizumab pegol 200 mg plus MTX gained an annual average of 52.1 full days of household activities compared to placebo with MTX. 30 Similarly, patients treated with certolizumab pegol 200 mg plus MTX in RAPID 1 gained an annual average of 42.0 work days greater reductions in pain (measured using a visual analog scale [VAS]) and fatigue (measured using the Fatigue Assessment Scale [FAS]) and improvements in health-related quality of life (measured using the Short Form 36-item Health Survey [SF-36]) were seen with certolizumab pegol plus MTX therapy compared to MTX monotherapy.…”

The impact of ankylosing spondylitis/axial spondyloarthritis on work productivity

“…The WPS is a disease-specific questionnaire designed to assess the impact of arthritis on workplace and household productivity, as well as daily activities during the preceding month. It is interviewer-administered or self-reported, and it covers a 1-month period [64]. The first item of the WPS addresses current labour market participation (employment outside the home), as well as providing normative and comparative data on employment status (not working implying complete loss of paid productivity).…”