The Work Productivity and Activity Impairment Questionnaire for Patients with Gastroesophageal Reflux Disease (WPAI-GERD): responsiveness to change and English language validation.
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BACKGROUND: A validated productivity questionnaire, the Work Productivity and Activity Impairment questionnaire for Gastroesophageal Reflux Disease (WPAI-GERD), exists for Swedish patients with GERD. OBJECTIVE: To assess responsiveness to change of the WPAI-GERD and construct validity of the English language version. METHODS: We used the WPAI-GERD in a before-after treatment clinical study of Canadian GERD patients with moderate or severe symptoms treated with esomeprazole 40 mg once daily for 4 weeks. We measured productivity variables including GERD-specific absence from work, reduced productivity while at work and reduced productivity while carrying out regular daily activities other than work during the preceding week. RESULTS: The analysis included 217 patients, of whom 71% (n = 153) were employed. Before treatment, employed patients reported an average 0.9 hours of absence from work due to GERD and 14.0% reduced work productivity (5.8 hours equivalent) in the previous week, as well as 21.0% reduced productivity in daily activities (all patients). After treatment, the corresponding figures decreased to 0.3 hours, 3.0% (1.1 hours equivalent) and 4.9%, respectively. Thus, the improvement (difference from start of treatment) in productivity was 0.6 hours (p = 0.011) for absence from work and 11.0% units (p < 0.001) for reduced work productivity (4.7 hours equivalent, p < 0.001). This translated into an avoided loss of work productivity of 5.3 hours in total on a weekly basis per employed patient. In addition, a 16.1% unit (p < 0.001) improvement for reduced productivity in activities was observed. Cross-sectional correlation coefficients of WPAI variables with symptoms (range 0.04-0.63) and health-related quality of life (HR-QOL; range 0.02-0.65) supported cross-sectional construct validity. Corresponding change score correlations between WPAI variables and HR-QOL (range 0.05-0.56) supported longitudinal construct validity of the WPAI-GERD while low change score correlations between productivity variables and relevant symptoms (range 0.06-0.34) did not. CONCLUSION: The English version of the WPAI-GERD showed good cross-sectional construct validity, and results indicated that the WPAI-GERD is responsive to change. Although the results also indicated that longitudinal construct validity may be poor, the overall findings suggest that further study of the instrument remains warranted.
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