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iterative process. While simple procedures and single-number estimates are appropriate for screening purposes in lower tiers of risk assessment, explicit disclosure of uncertainty and results from multiple scientifically plausible models are encouraged as part of upper tier risk assessment.

It is assumed in Appendix N-1 that the fundamental output of a risk assessment is a single estimate of risk: one number. We take a very different view, that risk assessment is a process for summarizing the available scientific information in both qualitative and quantitative form, for risk managers and for interested members of the public. Thus, regulatory decisions on managing risks should not be driven solely by single number risk estimates, but rather by a more comprehensive characterization of available scientific information, including uncertainties. We believe the CAPRA report strongly supports this latter interpretation.

An important aspect of risk management is the management of research directed at improving risk assessments by reducing uncertainty, permitting conservative assumptions to be superseded by more accurate models and observational data. The tiered approach to risk assessment and explicit consideration of both model and parameter uncertainties will facilitate identification of the opportunities for research that are most important for achieving the nation's health protection, environmental, and economic goals. We view debate over which conservative assumption to use in risk assessment as a poor substitute for an effective process to identify and pursue research that will improve regulatory decisions by reducing both the uncertainties and the need for the conservative assumptions.

Organization Of This Appendix

In this appendix, we discuss: 1) the role of risk assessment in supporting societal decisions on managing risk; 2) the use of "plausible conservatism" in selecting default options and alternatives to default options; 3) the use of an iterative approach in which specific science displaces default options; 4) the need for risk characterizations to be matched to their intended uses, and why a single quantitative estimate of risk may not be adequate; 5) why the process for conducting science-based risk assessments should be integrated and comprehensive; and 6) how risk assessments can serve an important role in guiding research to improve future risk assessments.

The Role of Risk Assessment in Supporting
Societal Decisions on Managing Risk

The development of risk assessments is one part of a larger process by which societal decisions and actions concerning risks are made. Risk assessments are that phase of the overall process in which all of the available information concerning exposure to the agent(s), the agent's(s') ability to cause adverse responses, and exposure-dose-response relationships, is synthesized into a risk

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