Yesterday, I posted on a working paper by James Galbraith and Travis Hale on income inequality and voting patterns. Andrew Gelman suggests that Galbraith and Hale have fallen prey to the ecological fallacy, in which one infers atributes about individuals from information about statistical aggregates about the group to which s/he belongs. (Thanks Abbas.)
But then they write:
We [Galbraith and Hale] can, however, infer that the Democratic Party has engaged in campaigns that have resonated with both the elite rich and the comparatively poor.
Well, no, you can’t infer that from aggregate results! To state it in two steps:
1. Just because state-level inequality is correlated with statewide vote for the Democrats, this does not imply that individual rich and poor voters are supporting the Democrats more than the Republicans. To make this claim is to make the ecological fallacy.
2. The Democrats do much better than the Republicans among poor voters, and much worse among the rich voters. (There’s lots of poll data on this; for example, see here.) So, not only are Galbraith and Hale making a logically false inference, they are also reaching a false conclusion.
Galbraith and Hale have revised their paper (see p. 12 and footnotes 19 and 20) in light of Gelman’s critique.