Presidential Election 2012 Results vs. Polls: Gallup Least Accurate Polling Firm, Rasmussen Also Fares Poorly, Says Nate Silver in Latest Analysis

By now it is clear that most polling firms overestimated Mitt Romney's support during the presidential campaign.

But a new analysis by Nate Silver at FiveThirtyEight shows the least accurate firm was the most well-known: Gallup.

Silver, of course, is the statistics maven who accurately predicted the outcome of the election in every single state, as well as Obama's large margin of victory in the Electoral College.

In the final weeks of the campaign, Gallup showed Romney in the lead by as much as 7 points, a result that no other firm ever found.

I've spent a lot of time talking about the Republican bias of automated "robocalls" conducted by some firms like Gravis and, most notably, Rasmussen, which became a darling of the right when it consistently showed Romney ahead in both the popular vote and important swing states.

By law, robocalls cannot contact cell phone numbers, whose users tend to skew younger and poorer, and therefore more Democratic.

Overall, firms utilizing automated polling did worse than firms that used live callers who could contact cellphones. The robocallers showed a Republican bias of more than 4 points.

But even the live-call firms showed Republican-leaning bias of nearly 2 points, plenty of error in an election with less than a 3-point margin of victory.

Gallup itself uses live callers, but its results skewed over 7 points toward the Republicans, making it the least accurate of any of the national polls.

The reasons for Gallup's error are still unclear.

It may be that there is some methodological issue with Gallup's polling, or the polling methods of the big firms in general. Perhaps Gallup's model predicting which respondents are actually likely to cast ballots is off the mark, as Gallup surveys of registered voters actually showed Obama in the lead by 3 points.

One very interesting result from the poll analysis: internet polls fared the best in predicting the outcome of the election.

Perhaps the best place to find people's true opinions is online.