Interspecies extrapolation in environmental exposure standard setting: A Bayesian synthesis approach

Currently the extrapolation of evidence from studies of non-human species to the setting of environmental exposure standards for humans includes the imposition of a variety of uncertainty factors reflecting unknown aspects of the procedure, including the relevance of evidence from one species to impacts in another. This paper develops and explores more flexible modelling of aspects of this extrapolation, using models proposed by DuMouchel [DuMouchel, W.H., Harris, J.E., 1983. Bayes methods for combining the results of cancer studies in humans and other species (with comment). J. Am. Statist. Assoc. 78, 293–308.] The approaches are based on Bayesian meta-analysis methods involving explicit modelling of relevance in the prior distributions, estimated using Markov chain Monte Carlo (MCMC) methods. The methods are applied to evidence relating chlorinated by-products exposure to adverse reproductive health effects. The relative merits of various approaches are discussed, and developments and next steps are outlined.