Effects of ambient air pollution measurement error on health effect estimates in time-series studies: a simulation-based analysis

• Authors: Matthew Strickland, Emory University; Katherine M Gass, Emory University; Gretchen T Goldman, Georgia Institute of Technology; James A Mulholland, Georgia Institute of Technology
• Journal Title: Journal of Exposure Science and Environmental Epidemiology
• Volume: Volume 25, Number 2
• Publisher: Nature Publishing Group | 2015-03, Pages 160-166
• Type of Work: Article | Post-print: After Peer Review
• Publisher DOI: http://doi.org/10.1038/jes.2013.16
• Subjects: Health Sciences, Epidemiology; Health Sciences, Public Health; Environmental Sciences
• Keywords: air pollution; measurement error; outdoor; time series; environmental health

Abstract

In this study we investigated bias caused by spatial variability and spatial heterogeneity in outdoor air pollutant concentrations, instrument imprecision, and choice of daily pollutant metric on risk ratio estimates obtained from a Poisson time series analysis. Daily concentrations for 12 pollutants were simulated for Atlanta, Georgia at 5 km resolution during a 6-year period. Viewing these as being representative of the true concentrations, a population-level pollutant health effect (risk ratio) was specified, and daily counts of health events were simulated. Error representative of instrument imprecision was added to the simulated concentrations at the locations of fixed site monitors in Atlanta, and these mismeasured values were combined to create three different city-wide daily metrics (central monitor, unweighted average, population-weighted average). Given our assumptions, the median bias in the risk ratio per unit increase in concentration was found to be lowest for the population-weighted average metric. Although the Berkson component of error caused bias away from the null in the log-linear models, the net bias due to measurement error tended to be towards the null. The relative differences in bias among the metrics were lessened, although not eliminated, by scaling results to interquartile range increases in concentration.