PIV did a post on the Bradley effect in May, see it here
The Bradley effect is a so called tendency of poll respondents to overstate their support for a black candidate thereby skewing the pre-election polling. The Bradley effect is a documented effect on polling in biracial contests that have occurred in previous election contests. It received its tag after a gubernatorial election in California, which Los Angeles Mayor Tom Bradley, an African American, was leading in polls just days before the election and lost.
Politico has a story today on over polling with the excerpt below, read it here
Respected polling analyst Mark Blumenthal found that during the Democratic primaries this year, preliminary exit polls overestimated Obama's strength in 18 of 20 states, by an average error of 7 percentage points, based on leaked early results.
