The disappearing Bradley effect

This is a VERY important study that rebuts the notion held by many (myself included) that Obama needs to have a big lead to win because lots of racist white voters lie to the pollsters.  While this might have been true at one time, it no longer appears to be:

A hot topic among polling nerds is the “Bradley effect,” which occurs when a non-white (usually black) candidate falls short of opinion polls on Election Day when he/she runs against a white candidate. For this reason it has been suggested that support for Obama might be overstated - a hidden bonus for John McCain. Now comes a large-scale empirical study (in preprint form) by Harvard political scientist Dan Hopkins. He finds that since the mid-1990s, the Bradley effect has disappeared. His paper is a must-read.

Many people believe that opinion polls overstate support for the black candidate, for instance due to latent racial bias that respondents are unaware of or will not report explicitly. The topic was mentioned in a recent article on racial bias by AP’s Ron Fournier, which did not contain relevant polling data but still sparked discussion.

The Bradley effect gets its name from former Los Angeles mayor Tom Bradley, a black man who lost the 1982 governor’s race despite the fact that in opinion polls taken before the election he led George Deukmejian, a white man. Sometimes it is also called the Wilder effect, after Gov. Doug Wilder of Virginia, who had a comfortable lead in led by nearly 10 percentage points in his 1990 campaign, but only won by a whisker.

Until now, the empirical evidence for the Bradley effect rested on individual cases. Such cases might suffer from biased assimilation, our tendency to more readily accept examples that favor our position. A counterexample (see pages 487 and 490 of this PDF) is the 1989 mayoral primary race in New York City between David Dinkins and incumbent Ed Koch. There, Dinkins, a black man, led Koch, a white man, by 0-5 percentage points in the closing weeks, only to win by 8 percentage points. Other counterexamples are available as well. Because of the mixed evidence, the Bradley/Wilder effect has been controversial. Gary Langer, director of polling for ABC news, has referred to the Bradley effect as “a theory in search of data.”

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The disappearing Bradley effect

September 27th, 2008, 1:03am by Sam Wang

http://election.princeton.edu/2008/09/27/the-disappearing-bradley-effect/

I’ll continue my consideration of factors that may systematically bias polls. Yesterday it was the effect of cell phone users, which I estimated could very slightly undersample Obama supporters. Today let’s consider latent racism.

A hot topic among polling nerds is the “Bradley effect,” which occurs when a non-white (usually black) candidate falls short of opinion polls on Election Day when he/she runs against a white candidate. For this reason it has been suggested that support for Obama might be overstated - a hidden bonus for John McCain. Now comes a large-scale empirical study (in preprint form) by Harvard political scientist Dan Hopkins. He finds that since the mid-1990s, the Bradley effect has disappeared. His paper is a must-read.