Friday, November 04, 2005

Presidential Approval since the Libby Indictment

Presidential Approval since January 1, 2005 with estimated trends and model fits.

President Bush's approval rating has fallen in the first six public polls taken after the indictment of Vice-President Cheney's Chief of Staff Lewis “Scooter” Libby on October 28. Based on a model of approval that takes into account the year-long decline in the President's approval rating, the effect of Hurricane Katrina and variation across polling organizations, I estimate the immediate decline since the Libby indictment as -1.59%. This compares with an estimate of -1.28% for the effect of Hurricane Katrina.

During the week that included the Libby indictment other events occurred which may have also contributed to the decline in approval. The press widely reported the 2000th U.S. military death in Iraq and the President accepted the withdrawal of his second Supreme Court nominee, Harriet Miers. Further, some of these polls interviewed respondents after the President nominated Judge Samuel Alito to the Supreme Court on October 31. It is not possible to separate out the effects of each of these individual events which all may contribute to the -1.59% estimate.

Since January 1, 2005, the President's approval has declined at a rate of -.031% per day. The immediate post-Libby indictment effect thus amounts to a 51 day drop in approval (-1.59/-.031). This compares to a drop equivalent to 41 days due to Hurricane Katrina and its aftermath.

While the decline of 1.59% is statistically significant, it is considerably smaller than the sudden drop of some 20% following the Iran-Contra revelation in the Reagan administration and the 10% drop in the Clinton administration during the Monica Lewinsky scandal. Both of those declines, however, occurred when approval was over 60% for both Presidents Reagan and Clinton. The estimated approval for President Bush as of October 27th was 40% in my model, suggesting that sharp declines may be somewhat less likely than for the previous presidents.

The recent polling results, along with previous polling, are available at

My model includes estimates of differences in approval across the various polling organizations. The estimated effects of Katrina, Libby and the long term trend are only slightly affected by ignoring these effects, though the inclusion of the “polling house” effects reduces the uncertainty of the estimated effects considerably.

One of these days I'll get around to posting on the house effects estimates. In the mean time, see Robert Chung's excellent pages on estimating these effects. His results and mine differ only modestly, though our estimation techniques are somewhat different. In my case, when looking only at the 2005 data, as here, I use a simple linear regression model with variables for date, post-Katrina and post-Libby plus indicator variables for each polling house. When modeling the entire Bush administration I use a different approach, closely related to the one Chung uses, though the approaches were developed independently of one another.

The model is based on 143 national polls by 17 different polling houses. There are 40 polls post-Katrina and 6 post-Libby. Three of these post-Libby polls are partially or completely overlapping at 39% approval in the figure. The six post-Libby polls included here are Associated Press-Ipsos poll Oct. 31-Nov. 2, 2005
ABC News/Washington Post Poll. Oct. 30-Nov. 2, 2005
Zogby America Poll. Oct. 29-Nov. 2, 2005
CBS News Poll. Oct. 30-Nov. 1, 2005
CNN/USA Today/Gallup Poll 10/28-30/05
ABC News/Washington Post Poll. 10/28-29/05
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