Statistical Modeling, Causal Inference, and Social Science is one of my favorite new blogs. It is primarily written by Andrew Gelman, a professor in the Departments of Statistics and Political Science at Columbia University.
A recent post looks at the difference between red and blue states and red and blue individuals. We all know that in the recent election poorer states tended to vote Republican while richer states tended to vote Democrat. On the basis of the famous maps many people jumped to the conclusion that poorer individuals were voting Republican (Nascar Republicans) while richer individuals were voting Democrat (trust fund Democrats). But the inference is a fallacy, the ecological fallacy. In fact, high-income individuals, as opposed to high-income states, vote Republican with greater likelihood than low-income individuals (the effect is not huge and it may be declining but it is significant).
It’s even true that rich counties tend to vote Republican with greater likelihood than poorer counties. Gelman links to this graph which nicely illustrates the ecological fallacy. The three lines show that within each state higher-income counties are more likely to vote Republican but when you look between states the correlation between income and voting Republican is negative. (Click to enlarge).