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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).
Within states, higher income counties vote republican, but when you pool the data across states, the reverse seems true. It's a great example of the weird (and incorrect) inferences you can come up with when you try to analyze data with pooled samples.