Anyone who has been on the page today has doubtless seen the spate of handwringing diaries on the Zogby poll jump for Bush. We were troubled by the fact that this came with the inclusion of the first night of polling after a debate which Kerry is essentially universally acknowledged to have won, and in which Bush made a major gaffe.
Were we wrong about the public perception of the debate? Was it just, as many have suggested, "statistical noise" or a "rogue sample"? Part of the problem is that I happen to think John Zogby is the best public pollster in the land, bar none. I tend to trust his results a lot more than I trust others.
One of the reasons that I trust Zogby is because he--in my view wisely--weights his polls based on partisan makeup. He doesn't breathlessly report that one candidate or the other is up 13 points because the sample included 12 percent more members of that candidate's party. This decision to weight leaves his polls open to gaming, however.
An example: Let's say Zogby weights to the much discussed 39D-35R-26I breakdown. Suppose a night's sample produces 40%Rs, 30%Ds, and 30%Is, with the Rs going 90-10 for Bush, the Ds going 90-10 for Kerry, and the Is splitting 50-50.
The raw result from that sample would be Bush 54-46. This is how Gallup would report it. After weighting, however, the result is Kerry 51.6-48.4 (39 * .9 + 35 * .1 + 26* .5).
Now, suppose that a fifth of the Republican base Bush respondents (8% of the total sample in this example) were to tell Mr. Zogby that they were DEMOCRATS voting for Bush. This means that the sample now includes 38% Dems, 32% Reps, and 30% Indys. The "Dems" now go for Kerry 71-29 (27-3 from the original sample plus the rogue 8, so 27/38). The remaining GOP goes for Bush 87.5-12.5 (was 36-4, now 28-4). The Indies are still 50-50
Now, the sample is weighted to a 54.9-45.1 Bush win, even more lopsided than the raw results.
Did this happen? Who knows? We do know that Bush's lead in that poll is due to a much higher level support among those calling themselves GOPers than Kerry has among those calling themselves Dems. Thoughts?