Mark Blumenthal | November 15, 2007
Topics: 2008 , Disclosure , Likely Voters , The 2008 Race
I have been focusing heavily on the Iowa caucuses, both our Disclosure Project started with polls there and because the competition, particularly on the Democratic side, is so intense. With a Democratic debate in Nevada tonight, we have had two new polls out of "likely voters" in the Nevada Democratic caucuses from Zogby and CNN.** Their results are quite different though for reasons that are probably explicable.
Both show Hillary Clinton leading, followed by Obama, Edwards and Richardson, in that order, but the percentages are very different. CNN shows Clinton leading Obama by 28 points (51% to 23%), with Edwards far behind (at 11%). Zogby shows Clinton with a narrower, 22 point lead over Obama (37% to 19%) with Edwards closer (at 15%).
The biggest obvious difference is that the CNN survey effectively pushed respondents harder for a choice. They show only 4% with no opinion, while the Zogby shows 17% as unsure. This is a very common source of variation across polls, leaving pollsters to debate which approach - pushing for a choice or allowing uncertain voters to register their indecision - is most appropriate when the election is still months away.
One likely contributor to that difference is that the CNN questions includes the job title of each candidate ("New York Senator Hillary Clinton," "Former North Carolina Senator John Edwards") which may frame the question a bit differently. Of course, since Zogby fails to disclose the full text of its vote question, we cannot know for certain.
But there is one other potential source of variation: How the pollster handles the expected low turnout. The CNN release tells us that they conducted 389 interviews with voters "who say they are likely to vote in the Nevada Democratic presidential caucus" out of a total sample of 2,084 adults. Thus, CNN screens rather tightly to identify a Democratic sample that represents 19% of Nevada adults. Once again, as Zogby fails to disclose it, we have no idea what portion of Nevada their sample represents (ditto for Mason-Dixon, ARG and Research 2000, the three other pollsters that have released Nevada surveys).
But at 19%, even the CNN survey may be a shot in the dark at the turnout in Nevada on January 19. In 2004, Nevada held traditional caucuses in mid-February that drew an estimate 9,000 participants (according to the Rhodes Cook Letter). That amounts to roughly one half of one percent (0.5%) of the state's voting age population at that time.
Of course, Nevada is switching to a party-run primary (the main difference being far fewer polling places). The states of Michigan and New Mexico have used a similar system, that produces a higher turnout than traditional caucuses (outside Iowa) typically get, but not much higher. The 2004 Democratic turnout, as a percentage of the voting age population, was 2.2% in Michigan and 7.3% in New Mexico (both events occurred a week before Nevada but a week after the New Hampshire primary).
So who turns out this time is anyone's guess. Will the voters sampled in these surveys bear any resemblance to those that turn out in Nevada on January 19? In size, at least, that seems very unlikely.
**Zogby has also released results for likely Republican caucus-goers. According to their release, CNN sampled likely Republican caucus-goers, but they have not yet released those results.