The report reflects congressional concerns about the evolving state of risk assessment, the uncertainty inherent in risk estimates based on theoretical models, the divergence of opinion within the scientific community on the merits of the underlying scientific evidence, and the large economic costs at stake in regulating the 189 air pollutants in question. The act also requested that EPA comply with the academy's methodological recommendations or explain in the Federal Register why it failed to do so. In response to each of these questions, the committee's major findings and recommendations are summarized below. Default options . Given this fact, the committee considered EPA to have acted reasonably in formulating default options for the purpose, and it recommended that the agency continue to use default options when dealing with uncertain models and mechanisms in risk assessment.
Data needs .
Although the health risks from a given pollutant may vary appreciably among individuals and among populations, the committee noted that such variability has generally received little consideration in EPA's risk assessments, in part because of limitations in the availability of pertinent data. To remedy this situation, the committee recommended that EPA and other federal agencies sponsor research into the causes and extent of interindividual variations in susceptibility to cancer and other diseases and that the results of such research be used to refine estimates of risks to individuals and population groups. Unless each of the various sources of uncertainty typically inherent in a risk assessment is adequately identified and explained, a decision-maker acting on the assessment may not know the extent of conservatism, if any, provided by the assessment. The upper-bound point estimates of risk typically computed by EPA, for example, do not convey the degree of uncertainty inherent therein. Risk communication .