REVIEWS AND COMMENTARIES Attributable Risk: Advantages of a Broad Definition of Exposure

Classification of exposure into two levels—one consisting exclusively of unexposed individuals and the other consisting of exposed and perhaps unexposed ones—yields an unbiased estimate of attributable risk when misclassification is nondifferential. The authors advocate, therefore, the use of a broad definition of exposure when estimating attributable risk. Based on this idea, they justify a simple and robust method for esti-mating the overall attributable risk from several exposures that is based on a division of subjects into two groups, a baseline consisting of those unexposed to all exposures and everyone else. Am J Epidemiol 1994; 140:303-9. bias (epidemiology); biometry; case-control studies; epidemiologic methods; occupa-tional exposure; odds ratio; sensitivity and specificity; statistics The attributable risk, sometimes referred to as the etiologic fraction or attributable risk proportion, is the fraction of observed cases that would have been avoided if no one in the population were exposed. The attrib-utable risk, just like relative risk, is sensitive to the definition of exposure, but the effects of the definition of exposure are not the same for the measures. In this paper, we re-view the effects of misclassification on es-timates of the attributable risk and propose Received for publication August 16,1993, and in final form May 6, 1994