Mark Blumenthal | March 28, 2008
Topics: 2008 , Barack Obama , Bradley/Wilder , Gallup , Hillary Clinton , Measurement , Rasmussen
Mickey Kaus has been arguing over the last week that the greater emphasis on racial issues in the Clinton-Obama nomination contest may have caused a return of the so-called Bradley-Wilder effect. The term refers to a pattern observed in the 1980s and early 1990s when the white opponents of African American candidates would do better on election day than indicated in pre-election polls (explained in more detail here, links to other sources here). Kaus thinks we may have evidence of a re-emergence of Bradley-Wilder in the results from the Gallup Daily and the Rasmussen Reports automated tracking surveys. Last Sunday, he wrote:
Gallup's national tracking poll has Obama retaking the lead over Hillary after bottoming out on the day of his big race speech. Rasmussen's robo-poll, on the other hand, shows Obama losing ground since last Tuesday. True, even Rasmussen doesn't seem to be putting a lot of emphasis on his survey's 6-point shift. But isn't this week's primary race exactly the sort of environment--i.e.., the issue of race is in the air--when robo-polling is supposed to have an advantage over the conventional human telephone polling used by Gallup? Voters wary of looking like bigots to a live operator--'and why didn't you like Obama's plea for mutual for understanding that all the editorial pages liked?'--might lie about their opinions, a phenomenon known as the Bradley Effect. But they might be more willing to tell the truth to a machine. ...
On Tuesday, I noted that the overall results from Gallup and Rasmussen were not that different when looking at data collected from March 14 (the day the Wright story broke) through the previous day:
- Live Interviewer Gallup Daily: Clinton +2 (47% to 45)
- Automated Rasmussen Reports: Obama +1 (45% to 44%)
Kaus updated his original post and responded that we should be focusing on the trends:
[I]f you look at the trend since Obama's 3/18 speech--which is what arguably charged the campaign with high-minded condemnation of racism and MSM sympathy for Obama of the sort that might produce a Bradley Effect--Obama gains 6 points in Gallup and loses 6 in Rasmussen through last Friday (and he's since lost one more on Rasmussen). That seems like a non-small difference. ...
He has continued to note the difference:
[3/25] Obama has now lost a net of 8 points on Rasmussen since the 18th, and 11 points since the 14th. On Gallup, he's gained several points.
[Yesterday] Bradley still in the race: Gallup (telephone poll) and Rasmussen (robo-poll) continue to diverge.
I have been puzzling over the trend and thought it would be helpful to post a chart of the data in question. In the chart below (click for a larger pop-up version), Kaus is focusing on the trends since the Obama/Wright speech on March 18. The dates on the chart are end-dates for each survey release. Keep in mind that Gallup reports a three-day rolling average, and Rasmussen reports a rolling four-day average, so the trend line reactions would theoretically lag slightly behind events.
If you overlook today's release, the chart does show a largely divergent trend, though most of the difference occurs in the three to four days after the speech. However, if you step back and look at the complete time series, the Gallup and Rasmussen lines are no more divergent now than they have been all along. In fact, if you remove three days of live-interviewer Gallup data -- the March 16-18 release which had Clinton (the white candidate) leading by seven points -- the divergent trend largely disappears.
Yes, for the last week, Obama has done better in the Rasmussen (automated) survey than the Gallup (live interviewer) data, but the difference is on the same scale as similar gaps since January that have see-sawed back and forth, favoring neither candidate consistently. So call me crazy, but I just don't see compelling evidence of a return of the Bradley-Wilder effect in these data, especially keeping in mind the potential for random variation in the trends.
One interesting pattern here -- and to be honest, I'm not sure what to make of it -- involves large gaps opposite of what we would expect from the Bradley-Wilder effect throughout much of January and again briefly centered on February 5/6 and March 18: At those times, the white candidate (Clinton) does better on the live-interviewer (Gallup) surveys than on the automated (Rasmussen) surveys. Also, as the charts below demonstrate, most of that difference occurs in the percentage supporting Clinton, not the percentage supporting Obama.
The difference in January may have had something to do with how the two surveys asked about other candidates still in the race, and the gaps afterward purely random, although that's a pure guess. Anyone have any better theories?