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Report of the Workshop on Selecting Input Distributions for Probabilistic Assessments

On May 15, 1997, the Deputy Administrator of the U.S. Environmental Protection Agency (EPA) signed the Agency's Policy for Use of Probabilistic Analysis in Risk Assessment. This policy establishes the Agency's position that such probabilistic analysis techniques as Monte Carlo Analysis, given adequate supporting data and credible assumptions, can be viable statistical tools for analyzing variability and uncertainty in risk assessments. The policy also identifies several implementation activities designed to assist Agency assessors with their review and preparation of probabilistic assessments. These activities include a commitment by the EPA Risk Assessment Forum (RAF) to organize workshops or colloquia to facilitate the development of distributions for exposure factors.

In the Summer of 1997, a technical panel, convened under the auspices of the RAF, began work on a framework for selecting input distributions for use in Monte Carlo analyses. Application of this framework to three exposure factors highlighted several issues. These issues resolve into two broad categories: issues associated with the representativeness of the data, and issues associated with using the Empirical Distribution Function (or resampling techniques) versus using a theoretical Parametric Distribution Function. These issues were the focal point for discussions at a workshop convened for EPA by Eastern Research Group, Inc. in April 1998. This report captures the main points and highlights the discussions held during the workshop. The workshop and this report will assist EPA in developing a framework and guidance for selecting input distributions for probabilistic risk assessments.

Contact: Risk Assessment Forum Staff (risk.forum@epa.gov), 202-564-6483

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Citation

U.S. EPA. Report of the Workshop on Selecting Input Distributions for Probabilistic Assessments. U.S. Environmental Protection Agency, Risk Assessment Forum, Washington, DC, 630/R-98/004, 1999.