Fine particulate air pollution and life expectancies in the United States: The role of influential observations

Changes in life expectancy (LE) across metropolitan areas in the United States have been associated with substantial differential reductions in fine particulate matter (aerodynamic diameter <2.5 m; PM2.5) air pollution that occurred during the 1980s and 1990s. It has been suggested that a single influential observation was largely responsible for the statistically significant LE-PM2.5 associations. In this paper, the role of influential observations is further explored. Stable and statistically significant LE-PM2.5 associations are observed in analyses that control for available socioeconomic, demographic, and proxy smoking variables and that use robust regression procedures that are relatively resistant to influential observations. These associations are not dependent upon the inclusion or exclusion of any single observation. Implications: These results contribute to the large and growing literature indicating that exposure to fine particulate matter air pollution has substantive adverse effects on human health. These results, however, also provide encouraging evidence that the improvements in air quality that occurred during the 1980s and 1990s contributed to measurable improvements in human health and life expectancy in the United States.