The Bradley effect, less commonly called the Wilder effect, is a proposed explanation for observed discrepancies between voter opinion polls and election outcomes in some American political campaigns when a white candidate and a non-white candidate run against each other. Named for Tom Bradley, an African-American who lost the 1982 California governor's race despite being ahead in some voter polls, the Bradley effect refers to an alleged tendency on the part of some voters to tell pollsters that they are undecided or likely to vote for a black candidate, and yet, on election day, vote for his/her white opponent.
The theory of the Bradley effect is that the inaccurate polls have been skewed by the phenomenon of social desirability bias. Specifically, some white voters give inaccurate polling responses for fear that, by stating their true preference, they will open themselves to criticism of racial motivation. The reluctance to give accurate polling answers has sometimes extended to post-election exit polls as well. The race of the pollster conducting the interview may factor in to voters' answers.
Some analysts have dismissed the theory of the Bradley effect as "baseless", while others argue that it may have existed in past elections, but not in more recent ones. One analysis of 133 senate and gubernatorial elections between 1989 and 2006 suggests that "before 1996, the median gap for black candidates was 3.1 percentage points, while for subsequent years it was -0.3 percentage points."
Similar effects have been posited in other contexts, notably the Shy Tory Factor and spiral of silence.