Nate Silver: “On average, the four tracking polls showed Mr. Obama with a 3.7 percentage point lead between the convention and the debate… Based on the numbers that the tracking polls published on Sunday, however, Mr. Obama’s lead was down to just 1.7 percentage points on average — a net shift of 2 points toward Mr. Romney since the debate.”
“But that calculation potentially underestimates Mr. Romney’s gains since only about two-thirds of the interviews in these polls were conducted after the debate. If Mr. Romney gained 2 points based on two-thirds of the interviews being conducted after the debate, that would imply a 3-point gain for him based on the post-debate interviews alone.”