Nate Silver, the numbers geek behind FiveThirtyEight.com, now an employee of the NYTimes, lays out 5 Reasons Republicans Could Do Even Better Than Expected
1. Downballot and cross-ballot effects.
2. Unlikely voters voted — and they voted Republican!
3. The incumbent rule, or something like it, makes a comeback.
4. The Scott Brown effect.
5. Likely voter models could be calibrated to the 2006 and 2008 elections, which were unusually good for Democrats.
You might find these arguments extraordinarily persuasive, extraordinarily unconvincing or somewhere in between. I think some are better than others, and I don’t really mean to “endorse” them.
What we know, however, is that polls can sometimes miss pretty badly in either direction.
Go and read Nate’s explanations behind each of the reasons. Maybe you’ll agree and maybe you won’t but he should make you think about “common wisdom”