consideration when making its decisions, and the uncertainties in those other components are also worthy of attention. Unfortunately, the uncertainties in these areas receive much less attention than those in the area of human health, both from EPA and from advisory bodies. Social factors, such as environmental justice, and the political context also play a role in EPA’s decisions and can have inherent uncertainties that are difficult to quantify.

This report strives to address this imbalance by giving attention to uncertainties in some of the factors that affect EPA’s decision making in addition to the uncertainties in the estimates of human health risks. Although the committee distinguishes among the different factors in this report, the factors are not independent, and the lines between them are often blurred. Technological factors can affect an economic analysis in a number of ways. The cost of complying with a regulation might be estimated in a technological assessment, for example, but typically it would also be discussed as part of an economic assessment. The consideration of susceptible populations can affect estimates of health risks, and the socioeconomic status of a population affected by a regulation can affect estimates of a “willingness-to-pay” analysis conducted as part of an economic analysis. The political context can affect, explicitly or implicitly, the relative considerations given to the different factors in a decision.

This increasingly complex set of issues requires agreed-upon principles and analytical tools for conducting the uncertainty analyses used in making environmental decisions. As developed in this report, the use of those new tools in the analysis of uncertainty poses new challenges and opportunities for EPA in making and communicating its environmental decisions.

This summary opens with a description of EPA’s charge to the committee and the committee’s approach to the charge, followed by an overview of three types of uncertainty. Focusing next on the multiple sources of uncertainty and their use in decision making, the summary presents highlights from each section of the report. This summary closes with the committee’s recommendations to EPA.


Statement of Task

EPA requested that the Institute of Medicine convene a committee to provide guidance to its decision makers and their partners in states and localities on approaches to managing risk in different contexts when uncertainty is present. It also sought guidance on how information on uncertainty should be presented to help risk managers make sound decisions and to increase transparency in its communications with the public about

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