Risk assessment: Evaluating error in subjective estimates

The Environmental Protection Agency (EPA) has responsibility to set uniform national air quality standards at the highest level which protects public health with an adequate safety margin. The precise point at which a standard is judgmentally set depends upon the scientific estimate of the exposure-response relationship for the pollutant of interest as well as value judgments regarding the point at which health effects are adverse, the meaning of adequate safety margins, and the size of a sensitive group within the general population. Because risk data is generally unavailable for the exposure levels of interest, subjective estimates based on related experience (e.g., animal tests, human exposures at higher levels) are needed for these risk estimates. This report describes many factors which have been observed to be sources of error or overconfidence when such subjective estimates are made. The implications of these factors are explored for each participant group and for alternative approaches.