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The answer to both questions is yes; Gallup is making some large assumptions in building its likely voter sample, assumptions that reduce the number of independents and inflate Republican numbers in that sample, in a year where we’ve been told by other pollsters that the GOP is less than enthused with McCain as their nominee and in a year where many independents will turn out. And who is around to question Gallup's assumptions? Not the media, as evidenced by the sorry Jill Lawrence story in the USAT.
Gallup Likely Voter Sample
July 25-27 USAT Poll
McCain Leads 49%-44%
Republican: 34%
Independent: 29%
Democrat: 36%
Keep in mind that no other pollster has shown McCain getting this much support. The registered voter numbers from this same poll that Gallup uses shows Obama leading by 3 points. And for comparison, take a look at the sample composition from their three-day tracking poll done at the same time:
Gallup Registered Voter Sample
July 25-27, 2008 Three-Day Tracking Poll
Republican: 29%
Independent: 33%
Democrat: 36%
In other words, Gallup is making large assumptions about who will be a likely voter, and driving those assumptions through their polls and into the media once again through many outlets. Gallup wants you to believe that if the election were held today, in the midst of McCain’s recent gaffes, that there would be a surge of GOP voters to his cause and a drop-off of independent voters. To their credit, Gallup notes that their assumptions about a “short-term energizing of the GOP base”, caused in their minds by the right-wing narrative that the media is unfair to McCain, could be only a snapshot in time, and not indicative of what will happen in November. But who besides Gallup is actually crediting this right-wing storyline of unfair media coverage with having any effect at all on a likely voter sample? Have other pollsters reached the same conclusions on this?
As I noted back in 2004, Gallup did the exact same thing with their samples to inflate the support for Bush at a time when other pollsters were not showing the same level of GOP support. However, since this was Gallup, and was being blasted around the world on CNN or USAT, it became the narrative used by the media.
Oh, and just for comparison, this is the sample composition of a Gallup poll just three weeks ago:
June 5-July 6, 2008 Poll
Republican: 21%
Independent: 38%
Democrat: 35%
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