… [O]ur forecast has moved toward Barack Obama over the past several days. It now gives him about a three-in-four chance of winning the Electoral College on Nov. 6.
I’ll explain a little bit more about how the model comes to that conclusion in a moment, but the intuition behind it is pretty simple:
1. Polls usually overrate the standing of the candidate who just held his convention.
2. Mitt Romney just held his convention. But he seems to have gotten a below-average bounce out of it. The national polls that have come out since the Republican National Convention have shown an almost exact tie in the race.
3. If the polls overrate Mr. Romney, and they show only a tie for him now, then he will eventually lose. [cont.]
Nate Silver, New York Times