Talking about polling…what has happened to Gallup?

The question is put by Nate Silver on his blog FiveThirtyEight after Gallup’s tracking poll is showing very different numbers than all other polls with Mitt Romney leading big.

While all the other tracking polls show a very even race, today’s Gallup figures show that Romney has increased his lead over Obama from 6 to 7 percentage points.

Under the headline “Gallup vs. the World,” Silver argues that this is not the first time that Gallup differs considerably from the others.

“Its results are deeply inconsistent with the results that other polling firms are showing in the presidential race, and the Gallup poll has a history of performing very poorly when that is the case.”

But that does not mean that Gallup should be ignored:

“You should consider it (Gallup) — but consider it in context. The context is that its most recent results differ substantially from the dozens of other state and national polls about the campaign. It’s much more likely that Gallup is wrong and everyone else is right than the other way around.”

Gallup’s numbers are included in Silver’s forecast which estimates Obama’s chances to win next month at 65.7 percent.