Friday, September 21, 2007

Bush Approval: 4 New Polls; Trend at 32.5%

We have four new presidential approval polls out this week that suggest a slowing of the recent upturn in President Bush's job ratings. The new data are a Pew Research poll done 9/12-16/07 with approval at 31%, disapproval at 59%, A CBS News poll done 9/14-16/07 with approval at 29%, disapproval at 64%, Zogby/Reuters conducted 9/13-16/07 found approval at 29% and disapproval at 71% and the Gallup/USAToday poll taken 9/14-16/07 which put approval at 36% and disapproval at 62%.

The result of these three new readings at the low end and one at the high end of recent polling moves the trend estimate to 32.5%. The blue trend line is still showing an upturn but the rate of increase now looks less steep. In comparison, the more sensitive red line estimator thinks approval has leveled off and is no longer climbing. However, red and blue estimates are in close agreement so we need more data to be confident about the leveling off. The situation is further complicated by the fact that three of the recent polls are from organizations whose polls typically have a negative house effect, meaning they tend to run a bit below the trend line. Gallup is the exception which is usually a bit above trend. The accident that 3 of the 4 new polls happen to come from houses with negative effects may mean we are overstating the amount of flattening in approval. This should become clear with a few more polls next week.

Also, don't overstate the size of the house effects here. None are very large. Zogby averages an effect of -2.4 (and uses an unusual 4 point question format that may contribute to this effect), while Pew and CBS are at -1.4 and -0.8 points respectively. Gallup is at +1.3. All those values are relatively small compared to the +/- 5 point spread we see around the trend estimator. (We'll be talking about house effects in more detail soon.)

At the moment we've seen quite a range of recent polls, with Zogby at CBS down at 29% while Gallup at 36% and Fox at 37% represent the high end. Still, this range of variation is about what we've come to expect and none of the recent polls is outside the 95% confidence intervals. So while politically there is a big difference between 29% and 37%, both are quite compatible with a "true" approval rating of 32.5%, given the normal randomness in survey results.

The last bit here is to look at the red dots in the figure below to see how the estimated trend has been changing over the past 20 polls. With only one exception, it has held between 32% and 33%. That is another reason to think that approval is flattening out now.