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A Different Approach: The Univ. of Iowa Caucus Poll

Topics: 2008 , Iowa , Likely Voters , The 2008 Race

A few additional notes on the poll of likely Iowa caucus-goers from the University of Iowa that we linked to earlier, based on information provided via email by U. of Iowa Assoc. Prof. David Redlawski:

First, the survey used a sample drawn from a list of Iowa households listed in telephone directories. As such, it has a potential coverage problem because it misses Iowans with unlisted telephone numbers. The survey screened to interview 907 self-reported registered voters.

Second, "because of a programming glitch," Redlawsk said he "cannot distinguish the 'no registered voters' from other refusals." However, we know that as of the fall of 2006, 84% of Iowa's adults were registered voters (1.9 million** registered voters divided by 2.26 million voting age adults).

Based on that statistic, we can make the following assumptions about the percentage of adults represented by the various subgroups reported on for this survey:

  • 425 Democratic Caucus Goers = 40% of adults
  • 319 "Most Likely" Democratic Caucus Goers = 29% of adults
  • 306 Republican Caucus Goers = 28% of adults
  • 223 "Most Likely Republican Caucus Goers = 21% of adults

In short, the various subgroups of likely caucus goers in the U. of Iowa poll represent a much broader slice of Iowa voters than the recent ABC/Washington Post survey or the Des Moines Register survey from last year.

Put another way, even the "most likely" caucus-goer definitions for this survey project to a combined Democratic and Republican turnout of 1.1 million participants - half the adults in Iowa. By comparison, Democratic turnout was an estimated 124,000 147,000 in 2004, and estimated Republican turnout was 108,000 90,000 in 1988.

Finally, even putting screening issues aside, this survey used an entirely open-ended vote preference question. Respondents had to volunteer the name of their choice without prompting. This method undoubtedly provides a tougher test of voter commitment, but also produces a much bigger undecided and renders the results incomparable to other Iowa polls. As such, we have not included either of the U. of Iowa polls in our Iowa charts.

**UPDATE: In doing these calculations, I should have added a decimal to the registered voter number (i.e. 1.97 voters rather than 1.9) which would have shown 87% as registered to vote rather than 84%. That change would increase my estimate of the percentage of adults represented by each sample to 30.6% for the "mostly likely" Democratic caucus goers and 21.4% for the "most likely" Republicans.

 

Comments
Andrew:

I don't think the universe of people with unlisted phone numbers would change the outcome of a poll surveying only those listed in the telephone directory. I can't think of a factor that would make these two groups have different preference.

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Joel:

What a dumb sampling method! They have all the disadvantages of using a list sample (non-coverage) plus all the disadvantages of RDD (relying on self-reports of registration and vote likelihood). Why on earth would they have used a phone list sample instead of a voter list sample? This is truly absurd -- voter list samples are easy to obtain and it is beyond sloppy and into weird territory to use a phone list sample for an election poll.

Add to that their even weirder choice of using an open-ended format for the crucial vote choice question and I entirely agree with your decision not to include UI polls in future analysis.

Thanks as always for the insight!

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Ted L. Loda:

Speaking about methodology, I don't believe any of the polls include voters who do not land line phones and rely exclusively on cell phones.

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