[Assessment of the impact of pain on work productivity: validation of the Spanish WPAI:Pain questionnaire].

BACKGROUND: Health measuring instruments are essential in daily clinical practice. However, a validation process is needed in order to certify the validity and reliability of it. The aim of our study is to validate a questionnaire to assess the consequences of pain in work productivity. METHODS: Based on the Work Productivity and Activity Impairment Questionnaire – General Health we have created a modified version called WPAI:Pain in order to be able to measure the consequences of pain in work productivity. The study was conducted following the usual guidelines of test validation, omitting face validity as WPAI:Pain is a modification of an existing questionnaire. Validity and reliability were calculated. RESULTS: A total of 577 questionnaires were obtained in 2 spanish university hospitals. The questionnaire's discriminating power was verified by Mann-Whitney test. Reliability tests were realized, Cronbach's alpha was 0.896 and Guttman split-half was 0.921. Stability was evaluated with a test-retest which was significant. Construct validity was established by Pearson correlation comparing the results of the questionnaire with the pain visual analog scale, which was statistically significant for all values. CONCLUSIONS: The WPAI:Pain questionnaire is a valid instrument for measuring the consequences of pain in work productivity.It is currently the only one validated in Spanish.Major studies are needed in order to establish its universal validity.