Just about everyone agrees that Republicans will be gaining a sizeable number of U.S. House seats come November, but this far in advance, few agree on the exact number. We’ve seen a couple of dozen predictions so far, and the range is from +10 GOP to +50 GOP—quite a spread.
To our knowledge, the Crystal Ball is the only predictive organization that uses two different methods for its prognostications. We carefully examine the 435 districts individually, and make an estimate of the outcome for each seat (using polling, past election results, elite opinion in the district, and so on). Last week we published our current estimate of GOP gains from this method: +27 seats.
This week we employ the other method, statistical regression analysis that uses variables such as the president’s Gallup Poll rating and the basic facts of the election. The author is Prof. Alan Abramowitz of Emory University, a frequent contributor to the Crystal Ball and one of the nation’s most distinguished political scientists. Prof. Abramowitz’s model for the 2010 House midterm election has been perhaps the most accurate of all political science models in projecting past midterm elections. As Prof. Abramowitz explains, the key variables in the 2010 election are the simple realities that (1) it is the midterm election of a Democratic presidential administration and (2) the Democrats are defending so many marginal seats—more than fifty that they added in 2006 and 2008, two exceptionally pro-Democratic elections.
His model has a result that will startle many of our readers: Republicans will pick up 37 House seats in November. That is remarkably close to the 40 seats the GOP needs to take outright control of the House.
Let’s remember that the gap between +27 and +37 seats isn’t great, especially when viewed from the perspective of February. Over the next eight months, we expect the numbers in both methods of analysis to vary a bit, up or down, and eventually to converge as we approach November 2nd. It is already obvious that 2010 is going to be a midterm election to remember.
— Larry J. Sabato and Isaac T. Wood, Editors
According to a statistical model that has proven highly accurate in forecasting the outcomes of congressional elections, Republicans now have a good chance of regaining control of the House of Representatives in November. The model uses four independent variables to predict Republican seat change in congressional elections: the president’s net approval rating in the Gallup Poll, the results of the generic ballot question in the Gallup Poll, a dummy variable for midterm elections that is positive in Democratic midterm years and negative in Republican midterm years, and the number of seats held by Republicans before the election. The following table shows the results of a regression analysis of seat change in 32 postwar House elections using these four predictors.
Estimates for House Forecasting Model
All of the estimated coefficients are in the expected direction and statistically significant. As expected, the more seats the Republican Party holds before the election, the fewer seats it tends to gain (or the more seats it tends to lose), the larger the Republican lead or the smaller the Republican deficit on the generic ballot, the more seats Republicans can expect to win, and the more popular the Republican president or the less popular the Democratic president, the mores seats Republicans can expect to win. In addition, regardless of the president’s popularity or the results of the generic ballot, the president’s party tends to lose seats in midterm elections.
Two of the terms in the model—the midterm dummy variable and the number of Republican seats before the election—measure structural conditions that are fixed going into an election. There is nothing that either party can do to alter those factors. The other two terms—the generic ballot and presidential approval—measure the political environment in the country, and they can change during the election year.
Based on the current values of the four predictors, the model predicts that Republicans will gain 37 seats in the House of Representatives in November—very close to the 40 seats that they need to regain control of the House. This forecast is fairly close to those of a number of prominent political analysts based on more informal judgments about the national political environment and opportunities for seat switches.
Contrary to many other analyses, however, the results of the forecasting model indicate that the main factors contributing to likely Republican gains in November are structural and do not reflect an especially negative political environment for Democrats. The current political environment only appears unfavorable for Democrats compared with the extraordinarily favorable environment that the Party enjoyed in both 2006 and 2008. The two structural variables in the model—previous Republican seats and the midterm dummy variable—predict a Republican gain of 38 seats, half due to the small number of Republican seats prior to the election and half due to the fact that 2010 is a Democratic midterm year. According to this model, the main reasons that Democrats are likely to experience significant losses in 2010 are the normal tendency of voters to turn against the president’s party in midterm elections regardless of the national political environment and the fact that after gaining more than 50 seats in the past two elections, they are defending a large number of seats, many in Republican-leaning districts.
Based on the latest readings on net presidential approval (approximately +5) and the generic ballot (tied), the national political environment is fairly neutral at the moment. Even under what might be considered a best-case scenario for Democrats, if President Obama’s net approval rating were to improve from a +5 to a +20, and Democrats were to regain a 10 point lead on the generic ballot, Democrats would still be expected to lose about 20 seats in the House. On the other hand, under what might be considered a worst case scenario for Democrats, if President Obama’s net approval rating was to fall from a +5 to a -20 and Republicans were to gain a 10 point lead on the generic ballot, Democratic losses would be expected to reach 54 seats in the House. So while the national political environment will clearly have an impact on the outcome of the House elections, under any plausible set of circumstances Democrats are likely to lose a substantial number of seats in November due to structural features that are already set.