Impact of measurement error on quantifying the importance of proximity to point sources of air pollution

This project was motivated by the investigation of the impact of primary oil and gas infrastructure on levels of air pollutants in western Canada. In the published models, we assumed that the distances between sources and air monitors were the key determinants of exposure and were measured precisely. These models related the logarithm of air pollutant concentration to a function of separation distance ("distance weight"). We undertook a simulation study to determine the impact on the observed source-pollutant association of uncertainty in the separation distance and the number of relevant sources per monitoring station. We observed that both the number of sources in the vicinity of the monitoring station and the extent of error in the estimate of separation distance influence the estimate of the slope of the source-pollution association. Measurement error tended to attenuate the association and degrade power, whereas the greater number of sources per monitoring station also led to a shallower observed slope. Attempts to correct the estimates of the slope were hampered by the non-standard nature of the frequency distribution of the difference between distance weights based on true and mismeasured distances. Our results revealed unanticipated challenges in the interpretation and estimation of the original analyses.