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Exposure Assessment Methods

Evaluation of exposure-response relationships is a crucial component in assessment of causes of cancer. Quantitative exposure assessment is therefore an essential element in high-quality epidemiologic investigations. Occupational and Environmental Epidemiology Branch (OEEB) investigators devote considerable effort to improving exposure assessment techniques and evaluating the reliability and validity of procedures used in cohort and case-control studies of occupational and environmental exposures. Below are a few examples.

Geographic Information Systems (GIS) Methods in Environmental Epidemiology

Epidemiologic investigations of environment-cancer relationships rely on accurate, quantifiable exposure measurements. Such studies may use Geographic Information Systems (GIS) and regulatory and other environmental monitoring data to complement retrospective surveys, which are sometimes limited by participants’ knowledge of exposures in their surrounding environments. Cancer studies have benefited from the increasing availability of historical air and water monitoring data, satellite imagery, census, commercial databases, and other geographic datasets that allow for reconstruction of residence- and other location-based exposures over a substantial portion of a person’s lifetime.

OEEB investigators implement GIS-based exposure assessments using georeferenced data resources and residential histories collected in our studies of environmental hazards and cancer risk. Our approaches include using GIS and spatial-analytic methods to characterize exposure to environmental risk factors, incorporating space-time-activity information in exposure assessments, and employing biological and environmental measurements for exposure validation. This work addresses important epidemiologic considerations in geography-based environmental exposure assessments, including residential mobility and time spent in various microenvironments, positional error, and the challenges of extrapolation over space and time. These approaches have been implemented in a number of DCEG and OEEB studies, including to assess drinking water nitrate exposure among private well users in the Agricultural Health Study, to estimate ambient air pollution in the Southern California Ultrafines Study, and to validate estimated dioxin exposure metrics.

Publications on the use of GIS Methods in Environmental Epidemiology.

For more information, contact Dr. Mary Ward or Dr. Rena Jones.

Industry-based Studies

OEEB investigators have developed state-of-the-art quantitative exposure assessment methods that maximized the available measurements and exposure determinant information to predict historical exposure levels in several studies including diesel exhaust in the Diesel Exhaust in Miners Study, benzene in a cohort study of Benzene-Exposed Workers in China, and specific pesticides within the Agricultural Health Study

Population-based Studies

Exposure Assessment Using Job Exposure Matrices

Job Exposure Matrices (JEMs) are an efficient way to assign exposure estimates in population-based studies and may be the only exposure assessment option when only job and industry are available for study participants. DCEG investigators develop methods to improve JEMs by incorporating databases of exposure measurements to calibrate JEMs across time and across jobs and industries. For example, in the Shanghai Women's Health Study, investigators developed a novel framework to systematically combine a JEM with historical measurements to calibrate JEM exposure ratings used to estimate historical benzene and lead exposure. 

Publications on the use of Job Exposure Matrices

For more information, contact Dr. Melissa Friesen.

Exposure Assessment Using Occupation- and Industry-specific Modules

Occupation- and industry-specific modules ask detailed questions about work activities and exposures within its population-based case-control studies to better capture within-occupation differences in exposure. Usually these module responses are reviewed job-by-job by an exposure assessor to assign exposure estimates. OEEB investigators develop methods to more efficiently and transparently assign exposure in studies that use modules and examine the validity and reliability of these methods. Decision rules that link questionnaire responses to exposure estimates have been developed to assess occupational exposures in US case-control studies, including metalworking fluids, diesel exhaust, lead and benzene. In an evaluation of the reliability of decision rule approaches we found that decision rule estimates of occupational diesel exhaust exposure for the New England Bladder Cancer Study had moderately-high agreement with estimates obtained from expert reviews of each job. Exposure estimates in the decision rules are data-driven wherever possible, including use of subjects’ answers to occupation and industry-specific modules and use of job group medians derived from module responses to assign exposure to those in similar jobs without a completed module. Intensity estimates are based on synthesis of publicly available data sources whenever possible (see next section). We have also developed a method to extract patterns in the questionnaire responses that predict an expert’s exposure assignments using classification and regression tree (CART) models. The extracted decision rules have been used to improve the transparency and efficiency of applying the exposure decisions to other study subjects.

Publications on the use of occupation- and industry-specific modules

For more information, contact Dr. Melissa Friesen.

Synthesis of Publicly Available Exposure Data Sources

To assist exposure assessment efforts, OEEB conducts comprehensive literature reviews for specific agents to identify when, where, and how much exposure to that agent was likely to occur. Exposure concentrations identified in these reviews are extracted into exposure databases that can be used to characterize exposure determinants, such as time trends. We extended the use meta-regression models to identify exposure determinants of published occupational and environmental measurements, which are generally reported as summary statistics, for several exposures, including lead, benzene, and pesticides.

Publications on the synthesis of publicly available exposure data sources

For more information, contact Dr. Melissa Friesen.

Use of Sensors and Smartphone Technologies

OEEB investigators use state-of-the-art technologies in field studies to characterize exposure, including use of direct reading sensors (e.g., black carbon, ultrafine particulate, PM2.5) and smartphone apps to collect work activity diaries.

For more information, contact Dr. Melissa Friesen.

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