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Take a look at the results of eight different polls released in the last few days. png 1) "Undecided" voters -- Obviously, the differences in the undecided percentage are about much more than the random sampling variation that gives us the so-called "margin of error," but they are surprisingly common. Differences in question wording, context, survey mode and interviewer technique can explain much of the difference. In fact, variations in the undecided percentage are usually the main sources of "house effect" differences among pollsters. The key issue is that many voters are less than completely certain about how they will vote and will hesitate when confronted by a pollster's trial heat question. How the pollster handles that hesitation determines the percentage that ultimately get recorded as undecided.
First, their trial-heat question, as reproduced in an online report, appears to prompt for "undecided" as one of the four choices. And just before the vote question, they asked another question which probably suggests to respondents that "undecided" is a common response: Q1. Thinking about the 2008 presidential election, which of the following best describes your thoughts on this contest? They try to word their questions, train their interviewers or structure their automated calls in a way to push voters toward expressing a preference. Most pollsters include an explicit follow-up to those who say they are uncertain, asking which way they "lean." The pollsters that typically report the lowest undecided percentages have probably trained their interviewers to push especially hard for an answer. And SurveyUSA, the pollster with the smallest undecided in South Carolina (1%), typically inserts a pause in their automated script, so that respondents have to wait several seconds before hearing they can "press 9 for undecided." But it is probably best to focus on the underlying cause of all this variation: South Carolina voters feel a lot of uncertainty about their choice. Four of the pollsters followed up with a question about whether voters might still change their minds, and 18% to 26% said that they might. So many South Carolina Democrats -- like those in Iowa, New Hampshire before them -- are feeling uncertain about their decision.
points out, "the last 24 hours" may count as much in South Carolina as elsewhere. Do they conduct interviews with live interviewers or with an automated methodology (usually called "interactive voice response" or IVR) that uses a recording and asks respondents to answer by pressing keys on their touch-tone phones. Three of the pollsters that released surveys over the last week (SurveyUSA, Rasmussen and PPP) use the IVR method (as does InsiderAdvantage), while the others use live interviewers.
Kaus) assumes that respondents alter or hide their preferences to avoid a sense of "social discomfort" with the interviewer. Without an interviewer, there should be little or no effect. In this case the difference seems to be mostly about the undecided percentage, which is lower for the IVR surveys. In the most recent surveys, the three IVR pollsters report a smaller undecided percentage (7%) than the live interviewer pollsters (17%).
Some say voters are more willing to cast a "secret ballot" without an interviewer involved, while others argue that those willing to participate in IVR polls tend to be more opinionated. If the Bradley/Wilder effect is operating, we would expect to see it on surveys that use live interviewers, but in this case, the lack of an interviewer seems to work in Obama's favor. He leads Clinton by an average of 17 points on the IVR polls (44% to 27%, with 19% for Edwards), but by only 9 points on the interviewer surveys (37% to 28%, with 17% for Edwards).
tell us their unweighted Democratic likely voter sample amounted to 33% the adults they interviewed), none of the pollsters have reported incidence data. So some of the variation in results may come from the tightness of the screen, but we have no way to know for certain. Three of the South Carolina pollsters (SurveyUSA, ARG and Rasmussen) typically use a random-digit dial (RDD) technique that samples from all landline phones. They have to use screen questions to select likely Democratic primary voters. As least two (PPP and Clemson) drew samples from lists of registered votes and used the records on the lists to narrow their sampled universe to those they knew had a past history of participating in primaries.
Differences in the likely voter selection methods mean that the South Carolina polls have differences in the kinds of people sampled for each poll. One of the most important characteristics is the percentage of African-Americans. It varies from 42% to 55% among the five pollsters that reported it (I extrapolated an approximate value for Rasmussen from their results by race crosstab). png Another important difference largely hidden from view is the age composition of each sample. SurveyUSA reports 50% under the age of 50, compared to 43% on the McClatchy/MSNBC/Mason-Dixon survey. PPP had an older sample, with only 23% under the age of 45. All of these surveys indicate quite a bit of uncertainty, both about who will vote and about the preferences that their "likely voters" express. Obama appears to have an advantage, but we will not know how large until the votes are counted.
png The South Carolina polling continues to show a substantial lead for Obama, while Edwards' rise hints that he could challenge Clinton for second place. At the moment, Clinton continues to hold a six-point advantage over Edwards, but Edwards has been rising while Clinton has been moving down. Obama, meanwhile, has been fairly steady at around 40-44% support, though with some hint of a small decline in the sensitive estimator. Note however that the Clemson University poll included here had an amazing undecided rate of 36%. That makes every candidate in their poll look lower than in all other polls that have a much lower rate of undecided. The level of undecided is quite sensitive to how the poll is conducted, including whether respondents are pushed as to whether they "lean" towards a candidate. The Clemson poll apparently didn't push at all among undecided voters. We'd be making a mistake to read their data as indicating a decline of support for anyone. A second place for Edwards would, of course, be good news for his campaign, while Clinton would no doubt argue she had conceded the state to account for a third place finish. But Edwards still has some ground to make up, and late deciding voters remain an unknown-- if they are unhappy with either Clinton or Obama, Edwards can benefit simply by not being one of them. This may be especially true among independents who vote in the Democratic race, and the expected handful of Republicans who show up. Obama has appealed to white voters in previous primaries and caucuses. The pre-election polls have found him getting as low as 10% of the white vote in South Carolina. The potential for racial polarization in this Southern state could damage his ability to transcend race as a basis of voting. Paradoxically, there has been speculation that Clinton can win the votes of black women, a result that could reduce polarization in the exit poll. We'll know much more about how voters decided by Saturday night.
automated survey in South Carolina (conducted 1/24) finds: * 595 Likely Democratic Primary Voters ( 4%) 44 Obama 24 Clinton 19 Edwards 14 undecided Among a subsample of African-Americans (51% of the sample), Obama leads Clinton 67% to 13%.
conducted 1/19 through 1/22 by Ron Lester & Associates) finds: * 600 Likely Democratic Primary Voters ( 29%) 37 Obama 27 Clinton 15 Edwards 22 Don't Know/Not Sure Among a subsample of African-Americans, Obama leads Clinton (53% to 21%).
tracking surveys of South Carolina (conducted 1/22 through 1/24) finds: * 811 Likely Democratic Primary Voters ( 34%) 38 Obama 25 Clinton 21 Edwards 0 Kucinich 0 Gravel 5 Someone else 7 Not sure Since the beginning of their tracking survey (conducted 1/20 through 1/22), Obama has moved from 43% to 38%, Edwards from 15% to 21%, while Clinton remains at 25%.
South Carol...
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