Tuesday, May 08, 2007

Bush Approval: NPR at 37%, Trend at 34.7%

The polls are really rolling in yesterday and today and they provide a striking contrast and hence a good lesson.

The latest to arrive is actually a bit old but only just released. The NPR poll conducted 4/26-29/07 is actually the sixth oldest of the recent polls. It found approval at 37% and disapproval at 59%. The NPR poll is the product of a bi-partisan team of Greenberg Quinlan Rosner Research (D) and Public Opinion Strategies (R). They sample likely voters, rather than adults or registered voters. This sample population mixes with house effects to generally puts the NPR poll about 1.9 percentage points above the trend estimate. In fact, the trend estimate is now 34.7 and NPR is 37%, a 2.3 point discrepancy which is reasonably close to what the house effect would predict.

The interesting comparison and lesson is that the Newsweek story over the weekend stressed a new all time low in approval of President Bush while other polling has failed to find any strong downward trend (except for a Harris poll taken 4/20-23 that also had approval at 28%.) In my trend estimator, when Newsweek was the endpoint, the trend estimator was pulled down to 33.2%. I warned then that Newsweek was an outlier and that an estimate of 34 or so was more likely. The flurry of new polls since Newsweek help reinforce that conclusion.

Here are the last twelve approval polls in order:

38 33 35 35 28 32 37 35 35 28 34 38

The mean is 34% and the median is 35%. The two polls at 28% stand out pretty strongly from the rest.

The lesson for interpreting polls is that a single poll does not a trend make. The strong interpretation Newsweek gave its poll, and the extra hype it got on Sunday talk shows, was not supported by other evidence. I stress that I'm complaining here about interpretation of poll results, and not about the poll itself. The Newsweek poll was an outlier, but outliers happen and that should not lead to a conclusion of anything other than a bad random outcome about the poll. The news story that was based on the poll, on the other hand, took the findings and made a very strong claim about approval at a new low when other evidence is clear that approval has not fallen into the 20s. One simply cannot ignore all other polls when making claims about a trend.

The ultimate irony of this is that Newsweek is right: President Bush IS at an all time low for his presidency, and has been since January! His stable approval rate of 33%-35% in my trend estimator is indeed the lowest of his presidency, and he has shown no signs of recovery (though no sign of further decline either.) But that all time low for the trend is 33-35%, not 28%. The desire to pick each poll number that happens to be well below the trend estimate and emphasize how low it is misleads us from attending to the central trend estimate which has far more to say about the actual level of presidential support. Each poll is a random draw around the trend. Some will be lower, some higher. But that poll to poll variation is largely random. It is the trend that captures the systematic path of approval.

And so I conclude as I did originally about the Newsweek poll. The best estimate of approval remains in the 33-35 percent range. At the moment the trend is at 34.7, but it could easily drop a bit with new polls, or possibly rise a little. My money is on an average of 34, for the moment.

Below are the usual poll diagnostics. I commented on these more extensively in the last two approval posts, so I'll not say more about them here.