There have been a lot of claims recently about the impact of redistricting on the 2012 congressional elections. Progressives are alarmed that Democrats won a majority of the House vote—roughly 51%—while falling a full 17 seats short of a majority. Such a discrepancy between the winner by votes and the winner by seats is rare, so it’s natural to assume that Republican gerrymandering—the process of drawing districts to advantage one interest over others—might be the culprit. Neuroscientist and election forecaster Sam Wang recently added fuel to the fire, calling the 2012 outcome “The Great Gerrymander.” He identified 10 states, most of them controlled by Republicans, as notable and egregious deviations from a fair outcome, suggesting that gerrymandering cost the Democrats 15 seats in the current House of Representatives and calling for redistricting reform to fix the problem. Wang’s conclusion resembles that of political scientist Nicholas Goedert, who suggests that the 2012 maps cost the Democrats 14 seats. Is this right? Has gerrymandering allowed Republicans to defy the will of the people? The crucial question to ask when deciding whether redistricting “mattered” is: compared to what? What is the alternative set of districts—the “counterfactual”—to which you’re comparing the current districts? Once we consider some other alternatives, these claims about gerrymandering aren’t as strong as they first appear.
What if we “re-run” the 2012 House election, but using the old districts? We have done that simulation, using the 2008 presidential vote in both the old and new districts to capture how the redistricting might have moved partisans around. If we assume that nothing else affects House election outcomes but the partisanship of the districts—in other words, if we allow redistricting to have its maximum possible effect—we find that the 2011 redistricting cost Democrats 7 seats in 2012. This is not nothing, but it’s far less than what the Democrats needed to take back the House and about half what Wang estimated.
The effect is even smaller if we incorporate other important factors. Incumbency is the most important of these: lots of Republicans who were running as challengers or in open seats in 2010—and then won—ran as incumbents for the first time in 2012. We know that incumbency is a powerful factor in House elections, bringing candidates greater visibility, adding to their campaign coffers, and deterring quality challengers from running. On average, an incumbent in 2012 ran five percentage points ahead of a non-incumbent candidate from the same party in a similar seat. Sixty-one seats were were decided by less than this margin.
Full Article: Redistricting didn’t win Republicans the House.