Validity of exposure data obtained by questionnaire. Two examples from occupational reproductive studies.

Exposure data from self-administered questionnaires were compared with independent information on occupational exposures in two studies of reproductive outcome. Agreement in the case-referent study concerning dry-cleaning work and tetrachloroethylene exposure was good. However, exposure reporting was indicated to be more accurate for the cases than the referents. Correction for misclassification slightly changed the odds ratio from 1.02 to 1.27 for nonspecific exposure and from 0.92 to 0.82 for tetrachloroethylene exposure. Missing information on the latter exposure was more crucial, since adding the employer information for such exposure increased the risk estimate to 1.24. In a prospective follow-up study, exposure information was validated in a sample of the study population. Reporting of heavy lifting appeared to be fairly correct, whereas the underreporting of chemical exposures was a problem. Validation of self-reported exposure data is desirable, and the direction and magnitude of possible misclassification bias should be evaluated in each specific situation.