WASHINGTON (AP) -- Voters who cast ballots in Tuesday's election had a strikingly similar demographic profile to those who voted in 2010 and weren't all that different from those voting in 2006. But how they voted this year was very different from years past. Exit polls are generally a bad way to measure changes in turnout. In addition to the usual concerns about sampling error in any poll, exit polls could show additional bias on some traits, such as race or population density. That's because the sample of precincts where voters fill out the surveys are chosen based on geography....