Printed in U.S.A. DOI: 10.1093/aje/kwg089 Response to Dr. Smith: Timescale-dependent Mortality Effects of Air Pollution

Time-series studies have indicated that there is an associa-tion between day-to-day variation in ambient air pollution concentrations and day-to-day variation in numbers of deaths, after data are controlled for more slowly varying confounding factors such as weather, seasonality, and long-term trends. However, the estimated coefficients in the time-series studies are uninformative as to the amount of life lost due to pollution exposure, particularly within susceptible populations (1). If individuals who were severely ill and were expected to die shortly were the only people affected by current levels of air pollution, reducing ambient concentrations would not necessarily increase life expectancy significantly. This phenomenon of only brief advancement of the timing of death has been referred to as “short-term mortality displace