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Alan Abramowitz on turning House votes into seats

Topics: Generic House Vote , House of Representatives

Emory University political scientist Alan Abramowitz sent out a useful analysis today that he's given me permission to post:

From fivethirtyeight.com today:

[T]here is another issue at hand: how much does the generic ballot really tell us about what will happen on Election Day? It might be the case that the generic ballot is fairly stable, but that doesn't necessarily mean it's all that useful an indicator. In addition to the fact that the consensus of polls (however careful we are about calibrating it) might be off in one or the other direction, there's also the fact that the thing which the generic ballot is ostensibly trying to predict -- the national House popular vote -- is relatively irrelevant to the disposition of the chamber, or the number of seats that each party earns. Instead, what we want to know is how the generic ballot translates into each of the 435 congressional districts; this is the sort of problem that we're hard at work upon.

Nate provides a lot of excellent analysis. But there are two pretty silly statements here. First, the generic ballot is a pretty good predictor of both the national popular vote and the national seat results. Second, the national popular vote is a very good predictor of the overall seat results. It definitely is not "relatively irrelevant" to those results. For all House elections since WW II, the correlation between national vote share and national seat share is a whopping .93:

Image001

For more on how the national vote translates into seats in the House, see Andrew Gelman and his co-authors on the 2006 and 2008 elections.

Update 8/19 10:01 AM: Silver responds here. For more on how the generic ballot can be used to forecast House election outcomes, see Abramowitz's 2006 PS article (PDF).

[Cross-posted to brendan-nyhan.com]

 

Comments
Mogando669:

recent years (04, 06, 08) show that GOP tends to ride above that linear line.

If we assume the same national vote share as '94 (highly plausible), based on that graph, can easily translate to anywhere between 56% (244) and 59% (256) of seats, meaning 66-78 gains. Of course that sounds beyond the high end of current projections.

But even replicating '94 1-to-1 means 52 seats gained. Either way it's a huge disaster.

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AlanSnipes:

I wonder if Alan can comment on the possibility that the seats that Democrats are defending this year, in contrast to 1994 are located in heavier Democratic areas than then.
For example, the latest NBC/WSJ poll showed Republicans ahead 52-31 in the south.
How many more seats can the Democrats lose in the south?
Could this mean that while Democrats will certainly lose seats, it won't be as bad as 1994 because of what I described above?
I don't know but I would like someone to test this hypothesis.

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CompCon:

Uber-liberals like Nate Silver are grasping at anything they can to deny they are drowning. He doesn't seem to care much about complete poll analysis - just poll analysis that proves his far-left political beliefs. Since all the polls show those political beliefs being roundly rejected - he is ignoring and rejecting those polls.

No, the generic ballot is not a 100% predictor of the seat count. And, yes, congress is elected district by district - not nationwide.

But you can't ignore how many individual democrat seats are in trouble. The best resource I have found so far is http://www.realclearpolitics.com/epolls/2010/house/2010_elections_house_map.html where the seats are shown one by one.

Realclearpolitics shows only 148 safe democrat seats and 164 safe republican seats. That means that 106 seats are "in play".

That's HUGE. Democrats have to win 70% of the in-play seats to hold the house. But when you look seat by seat, it gets incremently worse for the democrats.

How do those 106 seats break down? Only 15 of those are republican seats - 91 of them are democrat seats.

As bad as that looks, it gets even worse. 8 of those republican seats are in "likely GOP". 3 are in "leans GOP". 1 is in toss-up, 2 in "leans dem", and only 1 in "likely dem".

Let's say that all of the "likely GOP" goes to the GOP and all of the "likely dem" goes to the dems. That would add to the safe seats for a total of 173 for dems and 174 for GOP.

That brings it down to 71 seats that only lean one way or the other or are a pure tossup. Only 6 of those seats are republican. There are 65 democrat seats in big danger of being lost. The democrats have to hold 45 of those seats that are in danger in order to hold the house. In other words, they have to hold 63% of their high risk seats in order to hold the house.

How many polls show it likely that democrats are going to take 63% of seats where they currently don't have enough of a lead to even label them as "likely dem".

Based on all of that, we are looking at a minimum of a 45 seat loss that could easily reach 60 or more. There is almost no chance that the democrats are keepting the house - especially with Obama pissing off 73% of the voters by promoting a victory mosque at ground zero and using our tax dollars to pay for the fundraising for it.

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CompCon:

Test. These comment posting problems are getting ridiculous.

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AlanSnipes:

@CompCon:
You always start any criticism with someone with labels like "uber-liberal" as if by name calling you can discredit facts that you don't like.
Nate Silver is actually quite moderate. He predicted that Obama would win by 6.1 points, he won by 7.2

He predicted 350 electoral votes for Obama, he recived 365.
Nate Silver works with statistics and whatever his peraonal opinions are, he uses facts in his reporting.

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RAG2:

Even if the Republicans gain as many seats as they did in 1994, it speaks of diminsishing political power for the GOP--given that the country is in much worse shape, at least economically, now than in 1994. In 1994, we were in the middle of robust recovery--with unemployment numbers nowhere near 9.5%. If the Republicans need things to be really, really, really bad in order to get a majority of House seats, then their ability to appeal with their ideas and agenda is waning.

Moreover, most experts do not think the Reps will win the Senate; in any case, it would take significantly more wins than in 1994 to accomplish that. And if most of the Dem Senators picked off are Blue Dogs--as they probably will be--then the GOP, in the event it does win the Senate, will be in for a bitter taste of its own medicine in regards to filibusters. Reps have never had 60 Senate seats since 1932, and I don't see it happening now.

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