Thursday, November 03, 2005

CBS News Poll of Bush Approval

The latest CBS poll has Bush's approval rating at a Nixonian 35%, but the results are being questioned. In particular, Joe's Dartblog raises some interesting points about the composition and weighting of party identification.

The last page of the complete 19-page report finally gives up the goods: 259 Republicans were surveyed. 326 Democrats. (Already unacceptably inconsistent with the national makeup.) And then an astonishing 351 "Independents". That, of course, isn't all. Savvy surveyors need to weight their data in order to make the results more accurate. In CBS' case, this is done by cutting 36 of the Republican responses off the top, and leaving the Democrat responses intact. This isn't the regularly shifty 'party self-identification' factor. The data comes from a table which, presumably, reflects party registration. And even if the numbers are PSI, they are still far removed from reality.

The net result: a political poll consisting of 34.8% Democrats, 23.8% Republicans, and 41.4% Independents. And President Bush's "lowest" approval rating ever.

Fortunately we can see how much impact this had on the results since CBS provides results by party identification: 77 percent of Republicans, 11 percent of Democrats, and 31 percent of Independents approve of the job Bush is doing. Bush's overall approval rating is 35% in the weighted sample, but 37% in the unweighted sample. The weighting does hurt Bush's numbers, but only a bit.

But even without the weighting, Joe thinks CBS's numbers are sketchy:

Sampling is obviously never precisely commensurate with actual party distribution, but CBS' poll here is far off-base, as seen when compared to other polls and to CBS' previous polls. Take this one, for example, where 377 Republicans were surveyed, 376 Democrats and 330 Independents.

Using those numbers gives you a poll with 35% Republicans, 35% Democrats, and 30% Republicans. But even with that distribution of party identification, Bush's approval rating would only be 40%, just slightly above the 39% that Bush is averaging in recent polls. Given the margin of error in any poll, it seems hard to say that CBS's numbers are seriously out of line with other polls.

Update: The latest Washington Post/ABC News poll is out. It has Bush's approval rating at 39 percent and disapproval at 60 percent. In this poll, the party composition was 31% Democrats, 27% Republicans, and 38 percent Independents. What's interesting is that even with more Republicans and fewer Democrats and Independents in its sample, Bush's net approval rating is -21 (39-60), almost exactly the same as the -22 points (35-57) in the CBS poll.

No matter how you cut it, Bush is becoming deeply unpopular.

Update 2: Bush's support by party identification is almost exactly the same is both polls. In the CBS poll, 11 percent of Democrats, 77 percent of Republicans, and 31 percent of Independents approve of Bush. In the Washington Post poll, the numbers are 11, 78, and 33 percent, respectively. Comparing the Washington Post numbers to the 2004 exit poll numbers we can see where Bush has lost support. In 2004, Bush got 93 percent of Republican votes, 11 percent of Democrats, and 48 percent of Independents. His support (or rather, non-support) among Democrat's hasn't changed, holding steady at 11 percent. He's lost 15 points, or 16 percent of his support among Republicans. Most importantly, he's lost 15 points or 31 percent of his support among Independents.

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