Use of expert judgment in exposure assessment. Part I. Characterization of personal exposure to benzene

This paper presents the results of the first phase of a study, conducted as an element of the National Human Exposure Assessment Survey (NHEXAS), to demonstrate the use of expert subjective judgment elicitation techniques to characterize the magnitude of and uncertainty in environmental exposure to benzene. In decisions about the value of exposure research or of regulatory controls, the characterization of uncertainty can play an influential role. Classical methods for characterizing uncertainty may be sufficient when adequate amounts of relevant data are available. Frequently, however, data are neither abundant nor directly relevant, making it necessary to rely to varying degrees on subjective judgment. Since the 1950s, methods to elicit and quantify subjective judgments have been explored but have rarely been applied to the field of environmental exposure assessment. In this phase of the project, seven experts in benzene exposure assessment were selected through a peer nomination process, participated in a 2-day workshop, and were interviewed individually to elicit their judgments about the distributions of residential ambient, residential indoor, and personal air benzene concentrations (6-day integrated average) experienced by both the non-smoking, non-occupationally exposed target and study populations of the US EPA Region V pilot study. Specifically, each expert was asked to characterize, in probabilistic form, the arithmetic means and the 90th percentiles of these distributions. This paper presents the experts' judgments about the concentrations of benzene encountered by the target population. The experts' judgments about levels of benzene in personal air were demonstrative of patterns observed in the judgments about the other distributions. They were in closest agreement about their predictions of the mean; with one exception, their best estimates of the mean fell within 7-11 microg/m(3) although they exhibited striking differences in the degree of uncertainty expressed. Their estimates of the 90th percentile were more varied with the best estimates ranging from 12 to 26 microg/m(3) for all but one expert. However, their predictions of the 90th percentile were far more uncertain. The paper demonstrates that coherent subjective judgments can be elicited from exposure assessment scientists and critically examines the challenges and potential benefits of a subjective judgment approach. The results of the second phase of the project, in which measurements from the NHEXAS field study in Region V are used to calibrate the experts' judgments about the benzene exposures in the study population, will be presented in a second paper.