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DEALING WITH UNCERTAINTY ABOUT RISK IN RISK MANAGEMENT 56 original typesetting files. Page breaks are true to the original; line lengths, word breaks, heading styles, and other typesetting-specific formatting, however, cannot be About this PDF file: This new digital representation of the original work has been recomposed from XML files created from the original paper book, not from the retained, and some typographic errors may have been accidentally inserted. Please use the print version of this publication as the authoritative version for attribution. questions of regulatory action. In practice, such separation is difficult to maintain (see Bayer, in this volume), as illustrated by the tendency to use conservative assumptions in risk assessment when scientific uncertainties are large. This tendency reflects a societal consensus that conservatism is protective in risk matters. Attempting to separate scientific questions from policy questions is particularly difficult for low-level risks, because assessment uncertainties are great for these risks. For many exposures there is no direct evidence that risk exists; the evidence is only that risk exists for much higher exposures. Out of prudence we assume that low-level risks do exist and that thresholds do not exist. But this raises further difficulties, as John Gibbons (1983) notes: A zero-threshold situation leaves the policymaker in a great quandary. As long as there is some threshold level below which there are no ill effects, social equity can be preserved. But if dose and effect have a zero-zero intercept, then the policymaker must talk about determining acceptable risk, which is far more difficult to deal with than no risk. In other words, risk management has become much harder because we no longer believe in thresholds, at least scientifically. Here the de minimis approach can offer policy thresholds in lieu of scientific thresholds. Individual Versus Societal Definition of De Minimis Risk Certainly a society can manage risk to the population as a whole by limiting individual risks. This is, in fact, the approach taken by the Nuclear Regulatory Commission (1983) in its proposed safety goals for nuclear power plants. Individual risk limits are appropriate in cases where individuals face relatively high risks. But when individual risks are neither high nor inequitably distributed and the need for management arises because a large number of people face a low-to-moderate risk, then individual risk approaches can lead to misallocation of resources. To take a hypothetical example, a 10-6/yr risk of death to 1,000 people produces 10-3 expected fatalities per year, which is equivalent to an expectation of one fatality per thousand years. This same risk of 10-6/yr applied to the entire U.S. population of 230 million produces an expectation of 230 fatalities per year. If judgment of whether either situation represents de minimis risk is based solely on the degree of individual risk involved, the regulatory response (or nonresponse) to the two situations is likely to be comparable. Yet common sense tells us that greater effort and expenditure are justified to save 230 lives than 0.001 life.
