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METHODOLOGY FOR CHARACTERIZATION OF UNCERTAINTY IN EXPOSURE ASSESSMENTS
Citation:
Whitmore, R. METHODOLOGY FOR CHARACTERIZATION OF UNCERTAINTY IN EXPOSURE ASSESSMENTS. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/8-85/009.
Description:
Exposure assessments, except those based upon measured exposure levels for a probability sample of population members, rely upon a model to predict exposure. The model may be any mathematical function that estimates the population distribution of exposure or an individual's exposure as a function of one or more input variables. Whenever a model that has not been validated is used as the basis for an exposure assessment, the uncertainty associated with the exposure assessment may be substantial. The primary characterization of uncertainty is at least partly qualitative in this case, i.e., it includes a description of the assumptions inherent in the model and their justification. Plausible alternative models should be discussed. Sensitivity of the exposure assessment to model formulation can be investigated by replicating the assessment for plausible alternative models. When an exposure assessment is based upon directly measured exposure levels for a probability sample of population members, uncertainty can be greatly reduced and described quantitatively. The primary sources of uncertainty are measurement errors and sampling errors. A quality assurance program should be designed into the study to ensure that the magnitude of measurement errors can be estimated. The effects of all sources of random error should be measured quantitatively.