This is from Pollster.com today.
According to the release describing the Iowa State University poll we linked to earlier today, that poll “presents a much different picture the race than other recent polls.” More specifically, four recent surveys from the Des Moines Register, ARG, Rasmussen Reports and Strategic Vision all show Barack Obama and Hillary Clinton running within the margin of sampling error of each other, with John Edwards just a few points behind. The ISU survey shows Clinton (at 30%) with a comfortable lead over Edwards (24%) and Obama (20%). Why the big difference?
As we noted earlier today, the poll was conducted from November 6-18, which makes its results older than the four most recent surveys on our Iowa chart. However, according to ISU political science professor Jim McCormick, who directed the poll, “the biggest explanation for that is the volatility that still exists among those people who are likely to caucus.” A better explanation is the poll itself, which is very different than other recent Iowa caucus surveys.
-snip
The biggest difference involves the sample. It was drawn from the Iowa Secretary of State’s list of registered voters, but unlike every other Iowa poll that I’m aware of, ISU sampled only registered Democrats and Republicans, excluding the 36% of Iowa voters with no party registration.
Here’s why that omission is important: In the recent CBS/New York Times survey conducted in early November, registered independents were 19% of Democratic likely caucus goers and 13% of Republicans (and 19% of 2004 Democratic caucus goers, according to the network entrance poll). Among likely Democratic caucus goers, the independents were twice as likely to favor Barack Obama (37%) as registered Democrats (19%).
-snip
To be fair, as a percentage of all adults, the ISU samples of Democrats (12%) and Republicans (8%) are in line with most of the other recent surveys that have disclosed their incidence statistics to Pollster.com. But 20% to 25% of the respondents to those other surveys were independents. The omission of independents combined with the already dated field period helps explain why Obama scores lower in this survey.
http://www.pollster.com/blogs/more_on_the_iowa_state_poll.phpHere is the poll:
http://www.iastate.edu/~nscentral/news/2007/dec/caucus.shtml
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