Predicting EPA's forthcoming CO standards in light of new clinical evidence.

For the past several years, the EPA has been monitoring clinical studies on the adverse health effects of heart patients' exposure to carbon monoxide. This paper examines the impact of three such studies (including the multi-center CO study organized by the Health Effects Institute) on the forthcoming EPA standards for carbon monoxide. Eleven peer-nominated specialists with expertise in environmental science and public policy were interviewed according to a specific protocol. Overall, the experts felt that the HEI study would receive greater weight than the other two studies in the regulatory process for a variety of technical reasons. Weighting each expert opinion equally, we conclude that there is about a 0.69 probability that the CO standards will be retained at their present levels, a 0.28 probability that the standards will be tightened, and a 0.03 probability that the standards will be relaxed. When asked to imagine that the HEI data were never collected and then asked to reassess their probability judgments, the mean probability judgment that the standards will be relaxed rose to 0.11, while the mean probability judgment that the standards will be tightened fell to 0.20. A modest degree of variability in expert opinion is reported in the paper. While the HEI study may receive relatively great weight in the regulatory process, it increases only slightly the probability that EPA's CO standards will be changed.