Abstract
PP-29-049 Background/Aims: Our objective was to explore, through simulation, the effect of exposure measurement error on health effect estimates when ambient concentrations at subjects' residential locations are used as surrogates for total personal exposure to outdoor air pollutants. Methods: We used paired residence-based and mobility-based exposure estimates for 26,267 individuals in the South Coast Air Basin (SoCAB). Exposure estimates were based on a transportation survey conducted by the Southern California Association of Governments in 2000, and annual average concentration estimates from the CAMx dispersion model for nitrogen dioxide and hexavalent chromium. Modeled outdoor concentrations at home locations represented residence-based exposures. Mobility-based exposures were developed by geocoding the origin, destination, and likely route travelled for each individual record, extracting associated ambient concentrations, and weighting by time spent at each location and in transit. We simulated affected individuals by random assignment, increasing the proportion of individuals selected from the lowest to the highest quartile of mobility-based exposure. We then assigned a new quartile to each individual, using the residence-based exposure estimate. The ratio of the residence-based odds ratio and the mobility-based odds ratio indicates the amount of attenuation associated with the measurement error introduced by using a residence-based exposure estimate. Results: The odds ratios produced using the residence-based exposure estimates were between 30 and 50 percent lower than those produced with the mobility-based estimates. We repeated the random assignment of health effects using different proportions than in the first simulation, producing attenuation in the range of 10 to 60 percent. Conclusion: The use of a residence-based estimate as a surrogate for total personal exposure to outdoor air pollutants can produce substantial attenuation in health effect estimates. Careful consideration of geographic mobility is recommended when developing exposure estimates for mobile populations. Further simulation may aid in identifying factors determining the potential level of attenuation.
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