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Obama Will Over-perform Among Black Voters--trust Me

Mark Blumenthal picks up on something interesting in the South Carolina polls:

[Obama] leads Clinton by an average of 17 points on the IVR [i.e., automated] polls (44% to 27%, with 19% for Edwards), but by only 9 points on the interviewer surveys (37% to 28%, with 17% for Edwards).

Then, while discussing the Bradley Effect--in which some white voters tell pollsters they're going to vote for a black candidate but don't--he offers the following explanation:

One thing to note is that the so-called "Bradley/Wilder effect" ... 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. 

Put these two things together, and I think we have a possible test for my reverse Bradley-Effect hypothesis, which is that "some black voters would tell pollsters they support Hillary (or that they're undecided) because they don't want to sound like they're voting mainly out of racial solidarity, even though they actually intend to vote for Obama." The result of this would be that "polling understated support for the black candidate in a primary with a large African American population (i.e., Obama in South Carolina)."

If Obama consistently did better among black voters in automated polls, which eliminate the "social discomfort" that might discourage them from telling (presumably white) interviewers they support him, we'd have evidence for this hypothesis.

So what do the polls say? They say I might be onto something:

In the three most recent automated polls in South Carolina (PPP, SurveyUSA, and Rasmussen), Obama takes 67, 73, and 68 percent of the black vote, while Hillary takes 13, 18, and 16. In the three most recent live-interviewer polls (Zogby, Mason-Dixon, and ARG), Obama takes 55, 59, and 61 percent of black voters, while Hillary takes 18, 25, and 25.

So, among black voters, that's an average lead of 69-16 for Obama in automated polls, but only 58-23 in live-interviewer polls--a huge difference (53-point lead in the former; 35-point lead in the latter). It's not exactly definitive--I'm only using three data points in each case, and there are other methodological differences between the polls--but it does strongly suggest that some black voters are reluctant to tell human pollsters they support Obama, but feel comfortable saying it to a machine.

Anyway, we'll know soon enough. If Obama's final showing among blacks is 70 percent or more, both the robocallers and I will have something to crow about...

Update: Mickey Kaus speculates that voters might be inclined to lie to machines, contra Blumenthal's point above. It's plausible. But his theory doesn't explain the sharp divergence we see in South Carolina.

There are two possible scenarios that follow from Mickey's point. 1.) Black voters are lying both to humans and machines, in which case we'd need some theory to explain why they're lying to humans in such a way that lowers support for Obama, and to machines in such a way that raises it. 2.) Black voters are lying to machines and telling humans the truth, in which case we'd need some theory about why they're more inclined to be honest with a human, and why they'd overstate their support for Obama to a machine.

My hypothesis has the benefit of pleasing Mr. Occam, but I'm keeping an open mind...

Update II: Commenter lymonl makes a great point:

But aren't the exit polls all done by human beings, not machines?  How will you know how African-Americans really voted if they tell you on the way out that they voted for Clinton?  You wouldn't be able to attribute the entire disparity (heavier vote total for Obama than the exit polls indicated) because whites may have lied to exit pollsters too.  

Yes, the exits should be screwy, too. Though probably less screwy than the other polls, since people would have to lie more brazenly (about something they just did, not something they may or may not do in the future). Mickey says one way around this would be to examine precinct-by-precinct results. I agree. They should give us a better feel for the racial split since South Carolina's pretty segregated geographically. 

--Noam Scheiber