Quantifying the Bradley effect

Will the result be closer than the polls suggest? Up to now I haven't given much credence to the "Bradley effect" theory of latent racism, perhaps out of wishful thinking, but also because recent studies have tended to say the evidence does not support it. This article on VoxEU has given me pause.

Should Barack Obama worry about the Bradley effect? The much-discussed effect refers to observed discrepancies between voter opinion polls and election outcomes, in which African-American candidates receive a smaller vote share than would be predicted using opinion polls. In this column, I study US congressional and gubernatorial contests from 1998 to 2006 - black candidates on average receive a 2-3% lower share of the two-party vote than non-black candidates with similar numbers in the polls. If an effect of a similar size would appear in the current presidential race, then it would lower Obama's probability of winning from 85% to 53%.

In other words, it says the effect is small but real--real enough, in a race that is close to begin with, to alter the outcome. The study seems to be a careful piece of work, and it has an explanation for the fact that other studies have come up with a different answer. This election is very different from the ones in the study's historical sample, of course, so maybe the finding is barely relevant in any case. A disturbing read, nonetheless.