Nate Silver's latest posting concerns the algebra he ran to extrapolate the post Clinton polling from the current polling data from Gallup, etc.
He's getting numbers like Obama +10.5 in Gallup, Obama +8.9 in Ipsos.
Therefore his latest post is titled:
Sept. 8: Conventions May Put Obama in Front-Runner’s Position
it is possible to reverse-engineer an estimate of what Mr. Obama’s numbers look like in the postconvention part of the tracking surveys. Specifically, I will be looking to infer Mr. Obama’s numbers from interviews conducted after Bill Clinton’s speech on Wednesday night, which in my view was the pivotal moment of the convention... This can be determined with a little algebra if we know what percentage of the interviews in the Gallup survey reflect post-Clinton data. Fortunately, this calculation is fairly straightforward.Mitt Romney is out of touch and out of his league.
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.