"It was one of the best-known polling firms, however, that had among the worst results. In late October, Gallup consistently showed Mr. Romney ahead by about six percentage points among likely voters, far different from the average of other surveys. Gallup’s final poll of the election, which had Mr. Romney up by one point, was slightly better, but still identified the wrong winner in the election. Gallup has now had three poor elections in a row. In 2008, their polls overestimated Mr. Obama’s performance, while in 2010, they overestimated how well Republicans would do in the race for the United States House."One wonders if there isn't a correlation with the 1992 UK general election when the Tories scraped another win despite the polls suggesting everything would be going Labour's way. In the analysis, it became apparent that the public were embarrassed to admit they were voting Conservative and either lied or simply refused to take part, a kind of Obama version of Shy Tory Factor.
Politics Nate Silver takes a hindsight look at which polls were most accurate in the US election. He finds that most of them overestimated the Romney vote, especially Gallup:
Posted on Sunday, November 11, 2012