Mark Blumenthal | October 1, 2007
Topics: 2008 , Disclosure , The 2008 Race
Family obligations and a nagging cold virus kept me mostly off the grid this weekend while the blogs were abuzz over the latest Newsweek poll of Iowa likely caucus goers. So while late, let me add a few thoughts to those already offered over elsewhere.
First, the margins of sampling error reported by Newsweek -- +/- 7% for the likely Democratic caucus goers and +/- 9% for he Republicans - means that statistically meaningful conclusions are all but impossible regarding Barack Obama's "slight edge" (28% to 24%) over Hillary Clinton. Strictly speaking, even Mitt Romney's 9 point advantage does not attain the usual 95% confidence level that pollsters require to describe a lead as "statistically significant."
Noam Scheiber wonders about what the pollsters could say about the probability of an Obama lead among likely caucus goers, if not 95%. My best guess (assuming that the reported margins of error were based on the usual 95% confidence level) is that the probability of an Obama lead based on the Newsweek poll is about 50%. In other words, the odds of Obama "leading" on this poll are no better than a coin-flip, if we were to take repeated samplings of exactly the same design.
But Matt Yglesias makes the more important point:
It seems to me that there's no real point in arguing about the significance of the rather large +/- 7 points margin of error on this Newsweek poll . . . For something like this, uncertainty about the likely voter screen are probably going to be a bigger problem than sampling error anyway.
He is exactly right. Since July we have seen 12 public polls released in Iowa by 9 different organizations, and each appears to define and sample the likely caucus-goer universe differently. To the extent that pollsters have revealed the details, their snapshots of the electorate are poles apart, to say nothing of the candidates that those voters support. A month ago, for example, I found the percentage of first-time caucus-goers reported on four different polls of Democrats varying from 3% to 43%, with Edwards doing worse (and Clinton better) as the percentage of newcomers increased. The Newsweek survey reports 36% of likely Democratic caucus goers saying "this would be your first caucus."
Unfortunately, the Newsweek release omits many of the same methodological details left out of the other Iowa polling releases (including, remarkably enough, the number of interviews conducted with likely Democratic and likely Republican caucus goers). I have emailed Newsweek's pollsters the same questions we sent last week to the other Iowa pollsters and will include their responses when we begin reporting on the Disclosure Project
By the way, Yglesias also makes another important point: In a truly close race, the ultimate winner among the Democrats may depend on the second choices forced by the convoluted Caucus rules on those whose first choice fails to achieve "viability" (usually 15% of the vote) in their precinct. Remember that the official results for the Democrats will not be a head-count of the first preference of all caucus goers (as in a poll) but rather the estimated share of state delegates won by each candidate based on the final choices at the end of the night. So even if pollsters agreed on how to sample "likely caucus goers," the numbers would still be inconclusive in a close race.
Update:: Slate's Christopher Beam, who called just before I wrote this item, has more