The idea that air pollution is harmful is hardly new. However, critics of the previous research of Joel Schwartz, associate professor of environmental health at the Harvard School of Public Health, and other air pollution researchers have claimed that those who die from air pollution are the very ill who would have died within a few days in any case. This notion is sometimes referred to as “harvesting.” Using a statistical analysis that can factor out expected deaths, Schwartz debunked this argument in a study, “Harvesting and Long Term Exposure Effects in the Relations Between Air Pollution and Mortality” in the March 1, 2000, issue of the American Journal of Epidemiology. If it were true that people who died from air pollution would have died soon anyway, reasoned Schwartz, then there should be a correspondence between an increase in death rates during or immediately following a period of air pollution and a decrease in death rates a few days later. But it doesn’t work that way. “Unfortunately, it doesn’t work like that,” said Schwartz.