Tuesday, February 28, 2006

Bush Approval and the CBS Poll

Approval of President Bush through polling of 2/26/2006. The blue trend line is estimated approval using all polls. The red trend line omits the latest CBS News poll, taken 2/22-26/06.

President Bush has suffered a decline in approval after almost two months of stable approval ratings. The decline is from about 42% to about 40% approval over the past month. In the six polls completed the last two weeks of February, the Presidents ratings have seen a low of 34%, a high of 45% and four polls at 40%. Most of these polls were completed before the question of a Dubai company operating US ports erupted last week.

Among the recent polls, the CBS News poll is the lowest and is likely to be given special scrutiny. The effect of this poll on my trend estimates is about 1%-- including this latest poll would lower my trend estimate to 39% support, while excluding it makes the estimate 40%, a modest effect.
However, the CBS poll and the Cook/RT Strategies polls are also the two taken since the Dubai port issue came on the scene. Cook's approval rating for polling taken 2/23-26/06 is 40%, down sharply from Cook's 47% in late January (1/22-25). The CBS rating is down from 42% taken at almost the same time (1/20-25) as the Cook data. So while there is a gap between the two polls on the current level, both argue for a drop of 7-8% in approval since the State of the Union Address.

As readers of PoliticalArithmetic know, "house effects" across different polling organizations result in differences that tend to be persistent over time. In the graph above, the CBS News and New York Times polls (sometimes taken together and sometimes not) fall on average a bit below the trend line. While a number of CBS/NYT polls are right on the overall trend, others tend to fall below the trend by as much as 4%, given an overall house effect for CBS/NYT of about -2% compared to the trend. The current CBS poll is further below the trend that this average, but not exceptionally far from trend based on the polling since January 2005, as shown in the figure.

It is possible to do a more serious test for "outliers" to see if the new CBS polls is farther from the trend line than we could reasonably expect by chance. The results of this analysis are shown in the figure below.

The results show that while the latest CBS News poll is well below the trend, it is by no means a statistical outlier. It is inside the 95% confidence interval, though only slightly. Moreover, as the graph makes obvious, there have been a large number of polls further away from the trend than this one. My conclusion is that the low approval rating of 34% is not exceptionally low, and given the average CBS "house effect" does not seem out of line with past polls.

There is one other important issue for the CBS poll that will undoubtedly be much discussed: the balance of partisanship in the poll. Specifically the latest CBS poll finds Republicans to be only 28.4% of the sample and Democrats 37.4%. Compared to 2004 exit polls, which showed and even 37%-37% Republican-Democratic balance, the CBS polls appear to over-represent Democrats. In part this is a difference in samples-- the Exit polls are by definition samples of actual voters (which over-represents Republicans and under-represents Democrats) compared to the CBS sample of adults. And, of course, the "True" proportion of Republicans and Democrats is a continuously moving target that is moderately affected by question wording and varies over time. However, the CBS poll may somewhat over-represent Democrats, which would partially explain the house effect that we have seen.

What is not a major effect, however, is the shift in partisan composition between the January and February CBS polls. In January (1/20-25) the CBS poll found Approval at 42%, in line with other polling, and a partisan makeup of 29.3% Republican, 37.1% Independent, and 33.6% Democrat. In January approval was 34% with a partisan split of 28.4% Republican, 34.2% Independent and 37.4% Democratic. While the Republican figures didn't change much between the two polls, the Democrats gained a bit relative to Independents. But what impact does this have on the approval ratings? The CBS Poll breaks down approval by party identification so we can see what approval in February would be IF the partisan balance had remained exactly what it was in January. The answer: with February party id we get 33.73% approval. With the January distribution of party id approval would have been 34.88%. With rounding up in both cases, the difference in party id distribution makes only a 1% difference in approval. In short, while one might wonder about the CBS data's partisan split, they are NOT driving the 8% drop in the poll between January and February.

So what is? A drop in support across all party groups, but especially among Republicans. In January, approval among Republicans was 83%. In February it dropped to 72%, a shocking 11% decline among the president's base. Among Independents support fell from 34% to 29% and among Democrats from 14% to 9%, in both cases less than half the percentage point decline as among Republicans. This also compares to support among Republicans which had remained above 90% into early 2005.

It may be that this shock to Republican suppport is a short term effect, due perhaps to the security concerns raised by the Dubai port acquisition. Or to other recent problems of the White House including the House Republican's report on Katrina. But what is clear is that the decline registered in the CBS News poll is not simply a fluke or a large bias against the president. While the CBS poll is generally a couple of percentage points less favorable than the overall trend, the drop of 8% here, and the 7% decline in the Cook poll (not the absolute level of support, 34% in CBS, 40% in Cook) should send alarms ringing in the White House and in Republican Congressional circles. After a fairly good November and December, the Bush presidency appears once more to be slipping into the kind of poll numbers that suck all political capital out of negotiations with Congress, and that set the stage for especially difficult congressional and gubernatorial races in the fall.