Back in 2008, Gallup polls got wrong the size of a lead John McCain had in the election and now may be doing the same for Mitt Romney in 2012. The polling firm has Romney up by 7, the only polling firm to have him anywhere near such a lead.
In September of 2008 a Gallup poll had the then GOP candidate McCain 10 points up among voters most likely to vote, 54 to 44 percent. At that time McCain, after the GOP convention, did take a brief lead but no other polling firm had him up by more than 4 points. Obama eventually went on to beat McCain by 7 points, 53 to 46, winning 365 electoral votes to McCain's 173.
Over the past few days the Gallup daily tracking poll has built a Romney lead. Here again though, no other poll comes remotely close to a 7 point lead and some recent polls find Obama in the lead. The RealClearPolitics tracking of all the polls, despite Gallup's possibly inflated numbers, has the former governor of Massachusetts up by just one point over the president. Without factoring in the Gallup poll, it may in fact be President Obama leading.
Gallup polls performed poorly in 2008
Gallup ranked 17th of 23 polling firms for the 2008 election and have been well off in other recent elections. It's hard to pinpoint why they come up with such radically different numbers than those of other firms and we won't attempt to do so here but Thursday New York Times statistician and writer Nate Silver, who wrote the book The Signal and the Noise: Why So Many Predictions Fail-but Some Don't, suggested what may seem obvious.
"The context is that its most recent results differ substantially from the dozens of other state and national polls about the campaign," Silver wrote in the Times of Gallup's most recent polls. "It’s much more likely that Gallup is wrong and everyone else is right than the other way around."