Determining and Communicating the Uncertainty of Risk Estimates. Bernard D. Goldstein, Environmental and Occupational Health Sciences Institute, 681 Frelinghuysen Rd., Piscataway, NJ 08855
It has been suggested that the characterization of risk would be improved if a formal numerical uncertainty analysis was routinely performed and communicated along with a risk estimate. While there is general agreement as to the value of qualitative statements describing critical uncertainties in a risk assessment, there is opposition to the use of a more routine and formal mathematical approach to characterizing uncertainties. The opposition is based on the belief that a formal, quantitative approach is unnecessary, difficult to perform, and will not improve risk communication. Uncertainty is inherent in any estimation procedure. There are some sources of uncertainty, such as those related to estimating exposures, that are likely to be relatively easily addressed through the use of statistical methods. Other types of uncertainty, such as those associated with species-to-species or high-to-low dose extrapolation, are less straightforward or quantifiable. By characterizing the uncertainty and variability that underlie a potential risk, a distribution of risks can be generated instead of a point estimate. It should be kept in mind, however, that when data are scarce, assumptions about the underlying shape of a distribution will be needed--that is, when uncertainty is greatest, a range of probabilities based on assumptions would replace point estimates based on assumptions. Providing a numerical range of risk estimates reflecting uncertainty and variability may allow decisions to be made in a more informed and transparent manner than is possible when only a single point estimate is generated. However, communicating a range of risk estimates may be misconstrued by those unfamiliar with quantitative methods as implying that each of the numbers in the range is equally likely or plausible, and therefore valid for regulation. Many risk estimates performed at the state and local levels are crude yardsticks for decision-making. In this context, the routine provision of a range of risk estimates may only confuse and delay the regulatory process.