Polls predicted LA Mayor Tom Bradley, an African-American, would be elected California governor in 1982. His white opponent, George Deukmejian, won the election. This polling error gave rise to the term "Bradley Effect."
The "Bradley Effect" refers to voters telling pollsters they'll vote for a black candidate when they plan to vote for his white opponent. It is ascribed to what psychologists call social desirability bias, the desire to appear politically correct. In this case, it is the desire to avoid appearing racially biased.
Fast forward to the 2012 election. A variety of polls tell us Barack Obama is more likable than Mitt Romney. Perhaps they are accurate. On the other hand, perhaps the Bradley Effect is again at work. Maybe this is the political version of the old canard "some of my best friends are (fill in the blank)." Just saying....
