I think the Bradley effect may be driven by awareness of candidates.
For example: In Washington this year we had a supreme court race with very low visibility. Of the two candidates one was MUCH more qualified, and was expected to win by a solid amount. However results showed that he managed to only win counties in which he was either a known quantity or those which sent out voters pamphlets (the secretary of state this year didn't send them out due to budget cuts). In other words when voters have nothing to base their vote on except for the how someone's name looks on paper then the Bradley effect comes into play.
The race by the way was Gonzalez vs Danielson:
http://vote.wa.gov/results/current/Supreme-Court-Justice-Position-8_ByCounty.html
