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Beware Context-Free Election Analysis

Since the polls closed on Tuesday night, we've seen a rash of analysts focusing on a single vote or characteristic shared by a group of House candidates, without considering the context of those members' districts.
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Since the polls closed on Tuesday night, we've seen a rash of context-free analyses of the election results. Just as some commentators have interpreted the GOP's 60+ seat pickup as purely a backlash against Obama and his policies without considering the structural baseline, these analysts have typically focus on a single vote or characteristic shared by a group of House candidates without considering the context of those members' districts.

However, as John Sides notes, Democratic vote totals are very highly correlated with measures of district partisanship such as Obama's total in the district in 2008:

As such, any claim about influences on the election outcome needs to consider marginal effects relative to that baseline.

Here are just a few examples of how analysis can go wrong:

-NBC's First Read writes that "For all the talk of the Tea Party's strength - and there will certainly be a significant number of their candidates in Congress - just 32% of all Tea Party candidates who ran for Congress won." 32% sounds like a low number. However, most of the losing Tea Party candidates were running hopeless races against incumbents in heavily Democratic districts. Those in competitive districts seemed to perform about as well as other Republicans.

-Daily Kos campaign director Chris Bowers bashed conservative "Blue Dog Democrats," writing that "23 of 48 Blue Dogs standing for re-election have lost. Anyone who loses that badly doesn't get to tell Dems how to win." However, most Blue Dogs represented competitive districts and were thus most likely to be endangered by a GOP wave. The fact that they lost disproportionately doesn't mean that they were wrong about the Democratic message.

-Under the headline "Crushed," Josh Marshall noted that "Of the 39 Dems who voted against Health Care Reform, 12 are going to be returning in the next Congress," suggesting that opposition to reform was a cause of these members' defeats. However, he failed to note that most of anti-HCR members represented competitive districts and that vulnerable Democrats who opposed reform appeared to perform somewhat better than their pro-HCR counterparts.

-The Natural Resources Defense Council claimed to refute arguments that support for the cap-and-trade bill hurt Democrats by constructing the following graph:

Again, however, the opponents of cap-and-trade were more likely to represent marginal districts. The fact that they lost at higher rates doesn't mean that cap-and-trade didn't hurt its Democratic supporters.

For an example of a better approach, consider Eric McGhee's post on The Monkey Cage. Consistent with my finding that Democrats from competitive districts who supported health care reform appeared to perform worse on Election Day, he finds that House Democrats who supported health care reform, TARP, the stimulus bill, and/or cap-and-trade performed worse than those who did not controlling for the partisanship of their district. This finding directly contradicts the simplistic claims above about the effects of health care, cap-and-trade, and the Blue Dog agenda.

I replicated this estimate* and it appears to be robust. To illustrate the finding, here is a plot of the estimated marginal effect of an additional vote for one of the four controversial bills. I restrict my analysis to Democrats in potentially competitive seats (i.e. where President Obama received less than 60% of the vote in 2008):

The y-axis represents the estimated effect of an additional vote for a controversial bill on the predicted Democratic vote. The plot shows that this effect becomes increasingly negative as the district becomes less favorable to Democrats (lower Obama vote in 2008). While it is still very early, this finding contradicts the claims above, suggesting that the Democrats' aggressive legislative agenda may have provoked a backlash that was at least partly responsible for GOP overperformance in the House.

Update 11/4 9:09 PM: I should note that my Political Analysis article with Jacob Montgomery (PDF) reached a similar conclusion about the conditional effect of legislative extremism using a more comprehensive dataset:

[T]he effect of roll-call extremity on election results is moderated by party strength in the district (as measured by the CWBC presidential vote variable)... Substantively, these results indicate that members from very marginal districts suffer severe punishment for legislative extremity but the electoral cost of extremity declines rapidly as party strength in the district increases. In those districts in which the party is strongest, the marginal effect of roll-call extremity is actually either negligible (i.e. the 95% confidence interval includes zero) or positive. In other words, members are punished to the extent they are out of step with their district.

Update 11/5 7:52 AM: Chris Bowers objected to my quotation of his tweet above. I asked him to clarify his point -- here is what he wrote (compiled from a series of tweets):

The claim is that Blue Dogs have no special knowledge about how Dems can win elections. It's hard to phrase in a couple of tweets, but here goes... Basically, I don't think that the voting record or ideology of a Dem candidate mattered that much in electoral outcomes. What I do think is that the economic policies Blue Dogs prevented from passing would have helped Dem chances.

It's quite possible that a larger stimulus would have helped the Democrats; no arguments here on that point. As for the first claim, see above -- both Eric McGhee and I find that votes for highly controversial Democratic proposals may have hurt Democrats in marginal districts. But regardless of the merits of either claim, the fact that Blue Dogs lost disproportionately (Bowers's original point) is not evidence of much besides the fact that they represent swing districts.

* Like McGhee, I regressed the Democratic incumbent's vote total on an additive index of the number of the four bills that the member supported interacted with the two-party presidential vote for Obama in 2008. I also controlled for the district's Democratic House vote in 2008. However, I exclude the campaign spending variables McGhee included since they are potentially endogenous. I also exclude incumbents who did not have a Republican challenger.

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