Jay Cost: A Prediction for the 2006 House Contest

Two days ago, I began to discuss what I believe to be the best way to predict congressional elections. Developed first by Edward Tufte and later refined by Gary Jacobson, the “Tufte/Jacobson theory” is starting point I have chosen. It argues that we can predict the outcome of a congressional election based upon three factors: exposure, presidential job approval and changes in real disposable income per capita (RDI/cap). It is time to supply the details, supplement the theory with some extra concerns, and make a prediction for 2006.

Exposure is the extent to which the party of the President is above its historical average. For every 1% over its historical average, the party of the President tends to lose 0.76% of its congressional caucus in the next election, all else being equal. The Republican majority has averaged, since 1994, 227.33 seats. So, considering that today it enjoys 232, one might be inclined to assign a value of 2.01% to exposure. However, this would fail to account for the GOP mid-census Texas redistricting. Redistricting, from a national perspective, typically does not benefit one party more than another. However, the 1990 census resulted in a heavy and sustained Republican advantage – and Jacobson adjusted the exposure statistic to account for this Republican edge (by his estimate, 42 seats). We must do the same to account for the 2004 redistricting, which netted the Republicans four seats in the Texas delegation. This redistricting meant that the three net seats they gained in 2004 were not a consequence of a real expansion of their majority, but rather a slight shrinking of their majority counteracted by redistricting. If we control for this “inflation,” we would say that, in real terms, the GOP actually has one fewer seat in the 109th than it did in the 108th – 228 “real” seats. Accordingly, let us say that the GOP is overexposed by about 0.29%. Because every percentage over its historical average costs a party 0.76% of its delegation, we therefore expect this slight overexposure to cost the Republicans 0.22% of their delegation, all else being equal.

Next is presidential approval. History tells us that for every additional point of popularity a president enjoys in the final Gallup poll before the election, he increases the percentage size of his congressional party by 0.25%, all else being equal. The Gallup polls taken this year show Bush pulling an average of 42.0% approval. His approval rating obviously could trend in either direction in the next nine months. However, given the stability of his job approval since the beginning of 2006, I think it is fair to argue that he has largely stopped the hemorrhaging and that he will still be at about 42% approval on November 7. If this comes true, Bush’s popularity will yield an increase in the GOP’s congressional delegation of 10.50%, all else being equal.

The final important statistic is real disposable income per capita (RDI/cap). We are interested in its percentage change in the twelve months prior to the election. In the wake of Katrina, RDI/cap rose by a robust 3.7%. In the final quarter of 2005, it increased by a brisk 1.03%. Between 2001 and 2004, it increased by about 2% per year. It seems reasonable to conclude, given the pace of its growth in the fourth quarter of 2005 and recent history not affected by Katrina, that it will reach the 2% mark by election time. Though I am not an economist, this actually seems to me to be conservative. Indeed, for RDI/cap to reach a 12-month increase of 2% by October, it need only expand at 0.097% per month; this will not require much exertion for an economy whose GDP is expanding by more than 3% per year. In terms of congressional elections, every 1% increase in RDI/cap yields a 1.29% increase in the President’s party delegation. Thus, we can expect the state of the economy to boost the House GOP delegation by 2.58%, all else equal.

Finally, as I indicated yesterday, there is a baseline value. In other words, if you assume that the party of the President is neither over- nor under-exposed, that nobody likes the President, and that RDI/cap has neither grown nor shrunk in the last year, you can expect the party of the President to lose seats – specifically 17.7% of its delegation.

It is now a matter of simple arithmetic: 10.50% (presidential approval) + 2.58% (RDI/cap) - 0.22% (exposure) – 17.7% (baseline) = -4.84%. In other words, we can expect that the House Republican delegation will shrink by 4.84%. This means that, according to this theory, the Republicans will lose about 11 seats in November.

This is only the beginning of the story. It is not the end. Between 1946 and 2002, Tufte/Jacobson explains 70% of the variation in congressional elections – very good for political science work, but obviously far from perfect. So, the relevant question is: if we vary from this 11-seat mark, whom will the variation favor? The answer depends upon what kind of variation we are discussing – it can either be truly random variation or systematic variation. If it is truly random, then no theory can improve upon Tufte/Jacobson and we must leave things where they stand. If it is systematic variation, it means that the theory is currently missing an important causal process.

Truly random variation, e.g. the entire Texas Republican delegation catches encephalitis and cannot campaign, is impossible to predict and certainly extant to some degree in any process. If Tufte/Jacobson is a completely true theory of how congressional elections operate, and the only reason the real world varies from its predictions is because of random “noise”, a Democratic recapture of the House is improbable but not impossible.

However, I think there are regular processes out there that this theory does not capture, but that favor the Republicans. These should therefore cause this theory to overestimate Democratic gains. As I hinted yesterday, I think this theory serves as the necessary foundation for understanding what will happen in November, but it does not capture the entirety of the process. It excludes certain variables that will serve to mitigate Republican losses. This is a criticism of the theory, but it should not be taken to mean that we should dismiss what we have already developed. All good social science theories necessarily simplify the real world, boiling it down to the essentials so that we can understand the process that exists “out there”. Thus, we should understand the theory we have just reviewed as true but incomplete.

The first important variable that we have thus far excluded is the incumbency advantage. In the last fifty-five years, incumbents have increasingly shielded themselves from electoral mood swings. In other words, the incumbency advantage has expanded in the last half century such that most incumbent Republicans survive in anti-Republican years, and therefore seat changes in anti-Republican years are almost always via open seats. Scholars like Oklahoma University’s Ronald Keith Gaddie contend that exposure is less important than open-seat exposure – i.e. the number of net open seats that a party sports at election time. What matters is still the number of marginal seats a party has, but seats where incumbents are running tend not to be marginal. What of this year? Once again the number of open seats is minute – less than 5% of the House. David Wissing recently noted that there are 20 open seats (13 Republicans, 7 Democrats), only four of which (according to Stuart Rothenberg) are “strong takeover possibilities”. If Gaddie is correct and retirement is today the principal engine of partisan seat swings in Congress, we should not expect the Democrats to beat the 11-seat margin that we have outlined. They will likely net less than 10.

The second important variable that we have excluded has not yet been explored systematically by political scientists. Nevertheless, I think it is important. This is the tight alignment of the Republican electorate – the GOP’s set of voters is more aligned than it ever has been and it is more aligned than the Democrats’ set of voters. Until very recently, there were a large number of Republican-controlled congressional districts wherein voters chose Democratic presidential candidates. Today, there are a scant 17 congressional districts that voted for Kerry and a Republican member of Congress. Meanwhile, there are 41 congressional districts that voted for Bush and a Democratic member of Congress. While we cannot know for certain, this probably means that the distribution of his anemic popularity helps Bush. It is probable that anti-Bush voters are less likely to be located in Republican districts relative to other Republican presidents; pro-Bush voters are about as likely as ever to be located in Democratic districts relative to other Republican presidents. Thus, his job approval is probably more “efficient”, historically speaking, at protecting Republican incumbents, but still as efficient at damaging Democratic incumbents.

Are there other factors that are not captured by the model that favor the Democrats? None come to mind beside congressional job approval. The poor marks Congress currently receives are not captured by the Tufte/Jacobson model, but it is unclear that this will have a significant effect. As I mentioned previously, there has been initial work exploring whether people’s perceptions of Congress help or hurt the President’s party. However, it remains incomplete and there are important questions that linger. It also seems unlikely that the Abramoff scandal will harm Republicans in any significant way. Beyond Congress’s poor marks remain only Bush’s poor marks – which the Tufte/Jacobson theory captures and (probably) overestimates. There seem to be no strong causal processes that we have not yet discussed that would favor the Democrats. Indeed – we could probably tick off a few that additionally favor the Republicans: their strong money advantage, their strong mobilization advantage, the fact that they are not saddled with an ostensible incompetent like Howard Dean, etc.

Thus, we should consider an 11-seat swing in November as the maximum Democratic gain. Factoring in the incumbency pushes my estimate to less than 10. Factoring in the tight alignment of the electorate pushes my estimate to a Democratic gain of about 8 seats. Assuming that (a) Bush’s popularity does not drop off, (b) the economy does not stagnate and (c) Republicans do not have to defend more net open seats, I predict that the 110th Congress will have 224 Republicans and 211 Democrats.

Jay Cost, creator of the Horse Race Blog, is a doctoral candidate of political science at the University of Chicago. He can be reached at jay_cost@hotmail.com.

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You are right, cableguy. Jay Cost's Horsrace Blog was where I went every day during the two months prior to the election. He was right on, in nearly every state, analyzing which polls were valid and which were not as well as how past trends would play out in the present election. As I remember, he gave a little more credence to a Bush Pa. win then the final result would indicate. Other than that, his predictions were very good, especially Ohio, and made me feel confident going into November. Also, I remember he murdered the media idea that this huge army of disgruntled under 25's was going to rise up and make all the difference on election day.

And on election day, he cautioned all his readers not to take the exit polls seriously. He was not willing to accept that suddenly four or five million potential Bush voters woke up that morning and decided to vote Kerry. He was a stable ship of logic in a sea of media storm of misinformation.

Thanks for the ping! I like this guys results even though following his evaluation thought process is kind of like following an analyst's evaluation of whether a stock will go up or down. I'm a believer. If you have a ping list for this guy's analysis, please put me on it.
Thanks,
WMM

By far, Jay Cost was THE most accurate predictor in 2004. He clearly had OH, IO, FL, and NM going Bush, had PA, WI, PA, and NJ competitive, all on the basis of extensive voter registration anaylsis.

I'd take his prediction over any other, except my own :)

I do think he is somewhat negative here: a) Bush's job approval will go up some more; b) there are world events---given the Dem positions on things---that will ONLY help the GOP; and c) the Dems are particularly inept, even by recent standards.

Bottom line: GOP gains 2-4 House seats, 1-3 Senate seats.

Bottom line: GOP gains 2-4 House seats, 1-3 Senate seats.

That particular result would please me mightily. :) Keeping a simple majority also works for me. Thanks for your executive overview of Cost's 2004 track record.

The reason Cost was so accurate was that he actually took the time to meticulously examine population changes within counties in addition to simple voter registration numbers. He found that while the Dems indeed added significant numbers of new voters, they already lost similar numbers in the same districts due to population shifts. He didn't say, but I'm guessing that it was just one set of Dems moving out and a new set moving in. It was that level of analysis that allowed him to show that the GOP had, in fact, equaled or even out-registered the Dems in these states.

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