Exposure measurement error in PM_2.5 health effects studies: A pooled analysis of eight personal exposure validation studies

Abstract. Background: Exposure measurement error is a concern in long-term PM_2.5 health studies using ambient concentrations as exposures. We assessed error magnitude by estimating calibration coefficients as the association between personal PM_2.5 exposures from validation studies and typically available surrogate exposures. Methods. Daily personal and ambient PM_2.5, and when available sulfate, measurements were compiled from nine cities, over 2 to 12 days. True exposure was defined as personal exposure to PM_2.5 of ambient origin. Since PM_2.5 of ambient origin could only be determined for five cities, personal exposure to total PM _2.5 was also considered. Surrogate exposures were estimated as ambient PM_2.5 at the nearest monitor or predicted outside subjects' homes. We estimated calibration coefficients by regressing true on surrogate exposures in random effects models. Results: When monthly-averaged personal PM_2.5 of ambient origin was used as the true exposure, calibration coefficients equaled 0.31 (95% CI:0.14, 0.47) for nearest monitor and 0.54 (95% CI:0.42, 0.65) for outdoor home predictions. Between-city heterogeneity was not found for outdoor home PM_2.5 for either true exposure. Heterogeneity was significant for nearest monitor PM_2.5, for both true exposures, but not after adjusting for city-average motor vehicle number for total personal PM_2.5. Conclusions: Calibration coefficients were <1, consistent with previously reported chronic health risks using nearest monitor exposures being under-estimated when ambient concentrations are the exposure of interest. Calibration coefficients were closer to 1 for outdoor home predictions, likely reflecting less spatial error. Further research is needed to determine how our findings can be incorporated in future health studies.