Long‐Term Effects of Fine Particles on Mortality: Insights from 1984

I review an important study that Professor Evans published early in his career examining the role of cross‐sectional mortality studies in air pollution risk assessment. At a time when both risk assessment and particle effects on mortality were controversial, John's thoughtful analysis of the issues and data relevant to assessing long‐term mortality risks from airborne particles provides a comprehensive primer that is still relevant today. The paper includes a critical literature review, a meta‐analysis of published particle effect estimates, and a reanalysis of landmark cross‐sectional mortality data set. EPA criteria documents and related literature had largely discounted the cross‐sectional mortality findings on the basis of criticisms about exposure assessment and control for confounding. John's analysis reached a different conclusion, that is, “we are of the opinion that the cross‐sectional studies reflect a causal relationship between exposure to airborne particles and premature mortality. From our point of view it is as likely that parameters have been underestimated … as that they are overestimated due to confounding .” The paper acknowledged the impossibility of precisely quantifying the long‐term mortality effect of particle air pollution, and that there is a need for further research utilizing alternative approaches. These conclusions foreshadow the emergence, a decade later, of the influential particulate matter (PM) mortality findings from the Harvard Six Cities and American Cancer Society cohort studies. I conclude by suggesting that well designed cross‐sectional studies could play a role in identifying exposure–response associations in resource‐poor settings where there is a paucity of local evidence to support air pollution regulations.