Do Polls Break Towards the Challenger?

Nate Silver: “There are certainly some good reasons to think that the polls could break toward Mitt Romney. For instance, many polls out now were conducted among registered voters; when pollsters switch over to likely voter polls instead — which assess each voter’s probability of actually casting a ballot on Nov. 6 — it is likely that Mr. Romney will gain a point or two. And Barack Obama obviously has a lot of weight to bear from the lukewarm economic recovery.”

“But one hypothesis you should find less persuasive is the notion that the polls will break toward Mr. Romney just because he is the challenger. It is often asserted that this is the case — that the polls move toward the ‘out-party’ candidate rather than the incumbent. But in my view the empirical evidence — although it is somewhat ambiguous — mostly argues against this idea.”