FiveThirtyEight.com takes a look at the Bradley Effect.1
With that said, the evidence is pretty strong that the Bradley Effect in fact used to exist in the 1980s and probably through some point in the 1990s. …
The evidence is perhaps equally strong, however, that the Bradley Effect does not exist any longer.
It’s a good, brief look at racism and polling.
1 The Bradley effect: Telling pollsters you voted for an African-American candidate when you did not in order to disguise racial bias. Named for Los Angeles Mayor Tom Bradley, who lost the California gubernatorial election in 1982 when some polls, including exit polls, showed him winning handily.