Mark Blumenthal | February 25, 2008
Topics: 2008 , Barack Obama , CNN , Divergent Polls , Frank Newport , Hillary Clinton , USAToday Gallup
In the midst of a very busy day, the polling mystery de jour is certainly the dueling national Democratic primary results from Gallup. The new USA Today/Gallup poll out this afternoon (and conducted Thursday to Sunday, 2/21-24) shows Barack Obama leading Hillary Clinton nationally by 12 points (51% to 39%), while the latest Gallup "Daily" tracking release (conducted Friday to Sunday, 2/22-24) shows Obama edging Clinton by just two points (47% to 45%).
Our comments section and my email are overflowing with questions about why that may be. The answer is not obvious. Gallup editor-in-chief Frank Newport devotes an "editor's blog" item to this question (hat tip to Brian Schaffner who posted a link in the comments). Newport seems to be stumped:
There are some differences in the methodology between these two Gallup polls, including different days of interviewing and some differences in question order. But generally speaking, when Gallup conducts separate polls measuring the same variables at roughly the same times, the estimates are usually and predictably quite similar.
Sampling differences and the impact of random factors inherent in the survey process can sometimes explain why two polls are different. Given the similarities in the two polls' Republican estimates, however, I think the Democratic differences may well be another indicator of the conflicted nature of the Democratic race this year. It's not an easy choice, and as pre-election polls have shown in reference to the actual vote in some of the primary states, there is a lot of volatility out there among Democrats.
I have written quite a bit about the "hard choice" that Democrats face, and you can see continuing evidence of it in today's new Texas poll from CNN/ORC. Among likely Democratic primary voters in Texas, both Barack Obama and Hillary Clinton enjoy 80% favorable ratings. However, the mere potential for "volatility" does not explain as big a difference as is evident on the two Gallup results. It might take very little to shift vote preference but, in this case, what factors triggered the difference?
As such, I am curious about the "differences in question order" that Newport alludes to. It would be helpful to know what questions came just before the primary vote question on both surveys. One clue may be that the new USA Today/Gallup poll applies their standard "likely voter" model to the general election results. Gallup's model involves eight questions about past voting, vote intent, political interest and knowledge of voting procedures. Did any of those precede the primary vote preference question?
UPDATE - Gallup's Frank Newport clarifies: The Gallup Daily screen is a bit different from the procedure used for the USA Today/Gallup poll. Details -- and more information on the questions that came first on the USAT/Gallup poll -- now posted here.