TABLE B. Approaches for Dealing with Uncertainties in a Risk-Assessment Program

Program Model



Case-by-case judgments by experts


High potential to maximize use of most relevant scientific information bearing on specific issues

Potential for inconsistent treatment of different issues

Difficulty in achieving consensus

Need to agree on defaults

Written guidelines specifying defaults for data and model uncertainties (with allowance for departures in specific cases)

Consistent treatment of different issues

Maximizes transparency of process

Allows resolution of scientific disagreements by resorting to defaults

May be difficult

  • to justify departure
  • to achieve consensus among scientists that departures are justified in specific cases

Danger that uncertainties will be overlooked

Assessors asked to present full array of estimates, using all scientifically plausible models

Maximizes use of scientific information

Reasonably reliable portrayal of true state of scientific understanding

Highly complex characterization of risk, with no easy way to discriminate among estimates

Size of required effort may not be commensurate with utility of the outcome


EPA (U.S. Environmental Protection Agency). 1986. Guidelines for carcinogen risk assessment. Federal Register 51:33992–34003.

NRC (National Research Council). 1983. Risk Assessment in the Federal Government: Managing the Process. Washington, DC: National Academy Press.

NRC (National Research Council). 1994. Science and Judgment in Risk Assessment. Committee on Risk Assessment of Hazardous Air Pollutants. Board on Environmental Studies and Toxicology. Washington, DC: National Academy Press.

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