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Final Polls: About The Undecided?

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Well, for the umpteenth time this primary season, we wake up to wide variation on the final polls for the day's primaries. Today we have polls showing Barack Obama leading Hillary Clinton by anywhere from 4 to 14 points in North Carolina. Meanwhile, poll in Indiana show everything from a 2-point Obama edge to a 12-point Clinton blowout. One big question in looking at the variation is whether the pattern of variation suggests a pattern of a larger undecided translating into a hidden Clinton vote. The evidence on this question is mixed, however, and relies mostly on the results from just one pollster.

First, rather than listing the polls, lets do a chart of the final results in the last week or so from each pollster. Start with North Carolina. The following chart simply plots each result on a grid with the Obama percentage on the vertical axis and the Clinton percentage on the horizontal axis. All of the points on the North Carolina chart are above the blue diagonal line indicating an Obama lead.

Many -- such as one of Josh Marshall's readers -- think they see a pattern (which yours truly also saw at first in Pennsylvania but that subsequently disappeared) suggesting a coming "break" of undecided voters to Clinton. Such a pattern would imply a horizontal pattern to the dots above, with all of the variation in the Clinton number and little in the Obama number. That pattern holds only with respect to the Zogby poll, the one showing Obama leading by the biggest (51% to 37% margin), but also the poll with the most respondents categorized as either undecided or as choosing "someone else."

The pattern of the other points in North Carolina is mostly circular, about as varied as we would expect given sampling error and centered around a roughly seven point Obama advantage (50% to 43%) with 7% left over as undecided or "other."

Now Indiana:

In Indiana the dots are slightly more dispersed, with Zogby again the showing the best result for Obama, in this case a 2-point Obama advantage (45% to 43%), with 12% categorized as either undecided or "other." In this case, however, two polls have shown roughly as many voters choosing an option other than Obama or Clinton, although both were about a week old: One from TeleResearch (showing Clinton leading by 10 points with 14% undecided/other) and the other from Rasmussen Reports (giving Clinton a 5-point lead with 13% undecided/other).

Again, if we set the Zogby result aside, we get most of the polls forming a circular, mostly random pattern around an average advantage of 7 points (50% to 43%) with 7% undecided or "other."

In thinking about what to make about the difference between Zogby and the other polls, it may be useful to think about what it means for a respondent to tell a pollster they are "undecided" in the days leading up to the election. There are at least three possibilities:

  1. They are going to vote but are still uncertain about which candidate to support
  2. They are going to vote, have decided which candidate they support but are not willing to share their preference with the person (or computer) on the other end of the phone line
  3. They are not going to vote but were mistakenly identified as a "likely voter" by the pollster

Pollsters understand that many voters hover somewhere between a final decision and being totally undecided. So most consider it good practice to "push" uncertain voters, especially near election day, as the candidate they lean to supporting is almost always the candidate they ultimately support.

So I tend to agree with Pollster readers who have expressed frustration in comments with pollsters reporting a large undecided preference. What is especially puzzling about the Zogby result, however, is the very large percentage that they have reported as favoring "someone else" -- 4% in North Carolina (down from 8% over the weekend) and 5% in Indiana (down from 7%). What does that mean? Are respondents expressing a preference for John Edwards? John McCain? Are those really non-primary voters?

At any rate, given that the demographics of Zogby's samples are not radically different from the other pollsters in the two states, there is certainly a good possibility that a harder "push" would benefit Clinton. We also have seen in exit polls that late deciders have favored Clinton in most of the primaries since Super Tuesday. More on both states -- and particularly the issue of late deciders favoring Clinton -- later today.

Update: Just noticed this helpful information posted by Dick Bennett on the ARG web site:

The Democratic ballot in Indiana has two lines (Hillary Clinton and Barack Obama), while the Democratic ballot in North Carolina has four lines (Hillary Clinton, Mike Gravel, Barack Obama, and No Preference).

Democratic primary voters in our surveys in Indiana were asked just the two candidate choices. If voters said someone other than Clinton or Obama, our interviewers were instructed to inform the voters that there are only two choices on the ballot. In most cases, voters then selected Clinton or Obama instead of saying they were undecided.

In North Carolina, our surveys gave the four choices on the ballot. Democratic primary voters selecting the "no preference" line also told us that they would never vote for Clinton or Obama. Our results combine the no preference with someone else (even though no preference will get more votes than Mike Gravel).

In watching the results tonight, be aware that "someone else" is not on the ballot in Indiana and some voters in North Carolina will vote the no preference line.