Uncertainty due to low‐dose extrapolation: modified BMD methodology for epidemiological data

Traditional environmental risk assessment methodologies, including benchmark dose ( BMD ) estimation, were originally developed to be used with animal toxicology data. We discuss some problems that can occur when toxicology‐based methods are applied to human cohort studies, and we propose a new method for BMD risk estimation adapted to epidemiological data. Instead of extrapolating to zero‐dose levels to estimate risk in an unexposed population, our proposed alternative involves specifying a nonzero background exposure level instead. To account for uncertainty in that level, we can average modified BMD s over a distribution of exposure levels. We apply our modified BMD method to analyze data from a cohort study designed to assess the effects of prenatal polychlorinated biphenyl (PCB) exposure on cognitive ability in young children. Copyright © 2013 John Wiley & Sons, Ltd.