Preface -- Abbreviations -- Contents -- Summary -- 1 Introduction -- 2 Evolution and Use of Risk Assessment in the Environmental Protection Agency: Current Practice and Future Prospects -- 3 The Design of Risk Assessments -- 4 Uncertainty and Variability: The Recurring and Recalcitrant Elements of Risk Assessment -- 5 Toward a Unified Approach to Dose-Response Assessment -- 6 Selection and Use of Defaults -- 7 Implementing Cumulative Risk Assessment -- 8 Improving the Utility of Risk Assessment -- 9 Toward Improved Risk-Based Decision-Making -- Appendix A: Biographic Information on the Committee on Improving Risk Analysis Approaches Used by the Environmental Protection Agency -- Appendix B: Statement of Task of the Committee on Improving Risk Analysis Approaches Used by the Environmental Protection Agency -- Appendix C: Timeline of Selected Environmental Protection Agency Risk-Assessment Activities -- Appendix D: Environmental Protection Agency Response to Recommendations from Selected NRC Reports: Policy, Activity, and Practice -- Appendix E: Environmental Protection Agency Program and Region Responses to Questions from the Committee -- Appendix F: Case Studies of the Framework for Risk-Based Decision-Making.