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Political Geography and 2012 U.S. House Vote

- November 10, 2012

Yesterday at the Washington Post’s Fix blog, Aaron Blake observed that the Democratic Party appears likely to have won more raw votes in U.S. House of Representatives races, and yet fell well short of winning a majority of the seats.  Redistricting at work?  Blake thinks so:

The numbers seem to back up what we’ve been talking about on this blog for a while: Redistricting drew such a GOP-friendly map that, in a neutral environment, Republicans have an inherent advantage.

But partisan redistricting isn’t the only source of bias in the translation of votes to seats.  Consider a paper by Jowei Chen and Jonathan Rodden:

We show that in many states, Democrats are inefficiently concentrated in large cities and smaller industrial agglomerations such that they can expect to win fewer than 50 percent of the seats when they win 50 percent of the votes. To measure this “unintentional gerrymandering,” we use automated districting simulations based on precinct-level 2000 presidential election results in several states. Our results illustrate a strong relationship between the geographic concentration of Democratic voters and electoral bias favoring Republicans.

It’s not hard to find districts in which the Democratic House candidate takes more than 85% of the vote, even in states like California or New York where the GOP had no advantages in drawing district boundaries.  But it’s much harder to find contested races where the GOP candidate wins by those margins, suggesting that the Republican House vote is distributed more efficiently across space.  It’s not just about who draws the districts, but also about where Democrats and Republicans live in the first place.  Much more is in their paper.