The study methodology can t possibly produce the conclusion reached. The study is an ecologic type epidemiology study. Ecologic studies are designed to look for statistical correlations using demographic or population-level data, in this case county death rates and regional air pollution levels. In contrast to other types of epidemiologic studies, ecologic studies do not consider data on individuals, including how much pollution they were exposed to, their lifestyles and their actual causes of death. In the Hopkins study, not one death in the 20 counties examined was clinically attributed to air pollution.
Ecologic studies are subject to the ecologic fallacy.
The communities being compared likely differ in many factors. Any one or combination of those factors may be the reason for correlations identified. Jonathan Samet, the study s lead researcher, once discouraged the use of ecologic studies writing in the journal Health Physics that, The methodologic limitations inherent in the ecologic method may substantially bias ecologic estimates of risk. Even putting aside the ecologic fallacy, the study is dead on arrival. Another basic reality of epidemiology is that weak statistical associations are considered meaningless.