Bayesian methods for the cross‐design synthesis of epidemiological and toxicological evidence

Summary. Systematic review and synthesis (meta‐analysis) methods are now increasingly used in many areas of health care research. We investigate the potential usefulness of these methods for combining human and animal data in human health risk assessment of exposure to environmental chemicals. Currently, risk assessments are often based on narrative review and expert judgment, but systematic review and formal synthesis methods offer a more transparent and rigorous approach. The method is illustrated by using the example of trihalomethane exposure and its possible association with low birth weight. A systematic literature review identified 13 relevant studies (five epidemiological and eight toxicological). Study‐specific dose–response slope estimates were obtained for each of the studies and synthesized by using Bayesian meta‐analysis models. Sensitivity analyses of the results obtained to the assumptions made suggest that some assumptions are critical. It is concluded that systematic review methods should be used in the synthesis of evidence for environmental standard setting, that meta‐analysis will often be a valuable approach in these contexts and that sensitivity analyses are an important component of the approach whether or not formal synthesis methods (such as systematic review and meta‐analysis) are used.