David Strömberg

WH 2008 Analysis

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Last updated,

 October 1, 2008

The Bradley effect

I have estimated the Bradley effect based on 431 elections for House, Senator and Governor, 1998-2006, containing 26 black candidates. The effect is 2-3 percent of the two-party vote share. See Strömberg (2008) for details and discussion.

Below are some election statistics in case the Bradley effect for Obama is of similar size as that estimated in the 1998-2006 races discussed above.

• November 3 estimates.
• November 3 estimates:
  Democratic black candidates effect.
• October 29 estimates.

November 3

The table below show election statistics if Obama will suffer a Bradley effect of the same 2-3 percent size as the average (Democratic and Republican) candidates for the 22 House, Senate and Governor races 1998-2006 for which I have data.

November 3, black Democratic candidates

The estimated Bradley effect for black Democratic candidates lowers Obama's win chances as of November 3 from 87 to 68 percent. The effect is is -1.2 percent with a standard error of 1.6, so not statistically different from zero. Still, the uncertainty about the size of the Bradley effect makes Obama's lead uncertain.

I find this by using the full distribution of the estimated coefficient. I take a 100 draws from this distribution and estimate the average statistic.

October 29

The number below were computed using the 2-3 percent Bradley effect.

The polling data and vote data for elections with one black candidate is available here.