Nate Silver in the NYT:
The question now is not whether Mr. Obama will get a bounce in the polls, but how substantial it will be.
Some of the data, in fact, suggests that the conventions may have changed the composition of the race, making Mr. Obama a reasonably clear favorite as we enter the stretch run of the campaign.
On Saturday, Mr. Obama extended his advantage to three points from two points in the Gallup national tracking poll, and to four points from two in an online survey conducted by Ipsos. He pulled ahead of Mitt Romney by two points in the Rasmussen Reports tracking poll, reversing a one-point deficit in the edition of the poll published on Friday.
A fourth tracking poll, conducted online by the RAND Corporation’s American Life Panel, had Mr. Obama three percentage points ahead of Mr. Romney in the survey it published early Saturday morning; the candidates had been virtually tied in the poll on Friday. (The RAND survey has an interesting methodology — we’ll explore it more in a separate post.)
Nate goes on to note that Obama's bounce is based on incomplete polling - the polling included days before the Democratic Convention began and/or before Clinton spoke. So if you extrapolate from there, Obama's bounce is even greater:
Over all, that means that only about 30 percent of the data from the Gallup poll post-dated Mr. Clinton’s remarks.
If you do the math, it implies that Mr. Obama must have been leading Mr. Romney by 10 or 11 points in the minority of the poll conducted since Mr. Clinton’s speech for him to have gained three points in the survey over all.
In the table below, I’ve run through the same calculation for the other tracking polls. The results imply that Mr. Obama has run about nine points ahead of Mr. Romney in the portion of the Ipsos poll conducted since Mr. Clinton’s speech, about eight points ahead in the RAND poll, and about four points ahead in the Rasmussen poll.
