102 swing state polls within final 2 weeks from pollsters producing at least 4 polls. ARG, Rasmussen, Gravis and Pulse Opinion all showed a pro-Republican bias. Zogby, SurveyUSA, PPP, and ORC Intl showed no bias. Non-swing state polling was a slightly different story, but not of much importance in predicting who was going to win.
As others have said, the aggregators did indeed do a remarkable job of predicting the outcome, successfully correcting for biases where they occurred. They also got well ahead of the columnists in identifying when momentum shifted in the race; Republican spinners were still claiming momentum for Romney almost two weeks after the poll aggregators showed he was going backwards.
|Pollster||Polls||Mean polling error (MPE) in points||MPE standard error||prob. no bias|
|Pulse Opinion Research||5||REP+2.5||0.9||0.06|