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The assumptions made in answering these postulated questions should not be confused with the assumptions made in developing a baseline estimate of exposure or with the adjustments in parameter values made in performing a sensitivity analysis. The answers to these postulated questions do not give information about how likely the combination of values might be in the actual population or about how many (if any) persons might be subjected to the calculated exposure or risk in the real world.

A calculation of risk based on specific hypothetical or actual combinations of factors postulated within the exposure assessment can also be useful as a risk descriptor. It is often valuable to ask and answer specific questions of the "what if" nature to add perspective to the risk assessment.

The only information the answers to these questions convey is that if conditions A, B, and C are assumed, then the resulting exposure or risk will be X, Y, or Z, respectively. The values for X, Y, and Z are usually fairly straightforward to calculate and can be expresses as point estimates or ranges. Each assessment may have none, one, or several of these types of descriptors. The answers do not directly give information about how likely that combination of values might be in the actual population, so there are some limits to the applicability of these descriptors.


1. National Research Council. Risk Assessment in the Federal Government: Managing the Process. 1983.

2. U.S. EPA. Risk Assessment and Management: Framework for Decision Making. 1984.

3. U.S. EPA. Risk Assessment Guidelines. 51 Federal Register 33992-34054. September 24, 1986.

4. Presentation of Risk Assessment of Carcinogens; Ad Hoc Study Group on Risk Assessment Presentation. American Industrial Health Council. 1989.

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