December 5, 2008

Rich vs poor gap in Republicanism as a function of state wealth

Audacious Epigone has a post on the rich vs. poor gap in voting for McCain, as a function of the state's level of McCain support, and as a function of the state's wealth. For wealth, he used gross state product, which seems more difficult to measure than median household income. I took his index of the rich - poor gap in voting McCain and plotted it as a function of median household income:

As you can see, the richer a state is, the smaller the gap between rich and poor in voting for McCain. In poorer states, the rich are far more likely than the poor to vote Republican, compared to in richer states. (Spearman's rank correlation is -0.38, p = 0.008). This is as strong as the correlation A.E. found between the rich - poor gap and the percent of a state that voted for McCain. So, how rich a state is still tells us something about the size of the rich - poor gap: we explain 14% of the variation in the rich - poor gap by making it a monotonic decreasing function of state income.

A.E. defined "rich" as earning more than $100K, and "poor" as earning under $50K. Andrew Gelman, one of the authors of Red State, Blue State, Rich State, Poor State, showed similar results by cleaving the rich and poor as those earning above vs. under $50K. See here and a follow-up here.


  1. Good stuff. Of course, the racial component can't be dismissed--the percentage of a voting population that is black correlates with the political money gap at .45--stronger than income or McCain's overall showing. So presumably a lot of that divide is from blacks, disproportionately in the under $50k income category, voting for Obama. Fortunately, we have data for whites only by income, although only $50k- and $50k+. I'll take a look at that soon (if Andrew hasn't--I don't recall seeing it in the short time I've been following the book blog).

  2. Using the 'standard' Pearson correlation (which I default to unless otherwise noted), and median family income for '06-'07, a correlation of .48 between the political money divide and a state's median income. So I was wrong in asserting that Republican states show more of a political money divide than poor states do.


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