Understanding the Associations Between Statewide Diabetes Prevalence and Air Pollution Emissions

In a recent letter in Diabetes Care , Lockwood (1) presented a statistically significant correlation between statewide diabetes prevalence and statewide total air pollution emissions reported in the Environmental Protection Agency’s (EPA) toxic release inventory (TRI) database ( r = 0.54, P < 0.0001). Lockwood noted that such a correlation does not necessarily result from a causal relationship, but called for further research into understanding the association between air pollution and diabetes. In response, Nicolich (2) took issue with Lockwood’s use of statewide data. To demonstrate that correlations based on statewide data may not show causal relationships, Nicolich presented four highly statistically significant correlations between statewide diabetes prevalence and factors that would not be expected to be causal factors in diabetes: latitude of the state capital, longitude of the state capital, state population, and numerical position of the state name on an alphabetized …