Thursday, August 17, 2006

Bush Approval: Zogby at 34%

CORRECTION #2, 8/22: This story gets more amusing. The good folks at the sent me the topline results from the Zogby International poll. The difference in 34% (Zogby's website report of this poll) or 35% (PollingReport) ends up a matter of how you calculate and how you round. Zogby finds 96 respondents saying "excellent" and 256 saying "good" for Bush job performance. With 1018 respondents total, (96+256)/1018 = 34.5776, which rounds up to 35% in anybody's book. So why did Zogby say 34% on their website? If you compute the percentages for Excellent and Good separately, and round to a single decimal place, you get 9.4%+25.1% = 34.5%, which some would say should round to the even number, giving 34% as the approval number. So in this case I think both could make a case for their numbers. For me, I'd go with PollingReport's method-- you should never round intermediate results before rounding the final result. In this case the difference is small and doesn't substantially affect my results for the trend, especially since more polls are now available to leaven the effects of this one poll. Not tonight, but soon I'll change the data to 34.5% and redo the figures, but I'm not going to change the text below. Some things just aren't worth worrying about!

CORRECTION 8/17: The Zogby website reports approval at 34%, not the 35% at The Zogby site however does not give the disapproval rate for the entire sample. I've taken the 34% from Zogby, and report the disapproval at 65%, as does. I'll update this further if needed. The graph and text below has been updated to reflect the correct 34% approval rating reported by Zogby. This change shifts my approval trend estimate from 36.76 to 36.62. Thanks to an anonymous reader for pointing out the error.

A new Zogby poll, conducted 8/11-15/06 finds approval of President Bush at 34% with disapproval at 65%. This is a two point decline from Zogby's previous poll of 7/21-25. With Zogby added to the data, the trend estimate falls to 36.6% approval.

The shift to a negative trend is no longer overly sensitive to the very low (33%) approval rating in the recent AP poll. Without that poll the blue trend line is still moving in a small but clearly negative direction.

There is also considerable variation in recent polling, which ranges from 33% to 40%. Some of that is due to the different polling organizations doing the surveys. Four of the last six polls are from organizations with negative "house effects", meaning their polls typically fall a couple of points below the average approval across all polls. Two of these (Fox and Gallup) usually fall a little (less than 1 point) above the average. The result is some differences between polls that seem substantial but which actually fall within the normal range of error around the estimate of 36.6%.

The downturn in approval is still small, but compared to two weeks ago when the trend still seemed to be up, this represents an important turning point for approval. The precise turning point cannot yet be well estimated.

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