Wednesday, November 07, 2012

How well did 538 and RCP do in predicting the election results?

Q: How did the two major "poll of poll" sites do in predicting the election?

A: Quite well

RCP called every single state correctly of the 49 which have now been decided - BUT - they called Florida for Romney and that may (or may not) turn out to be wrong.

FiveThirtyEight's final prediction was: Obama 50.8, Romney 48.3. As of this moment, Obama is running 50.4, Romney 48.2. The "most likely" electoral scenario was 332 for Obama, which may turn out to be exactly right if President Obama holds Florida.

In other words, each of these two sites is 49/49 so far. Since they made different calls on Florida, one of them will ace all 50 states, and the other will be 49/50.
Q: How did the individual polling companies fare on the popular vote?

A: Mixed bag

Among the individual polling services, the closest was Google Consumer Surveys (who saw THAT coming?), which may end up getting it exactly right. They called it +2.3 for Obama, and the President is now running +2.22. Also right on the mark, since they don't use decimal places: Ipsos/Reuters and PPP, who called it +2. (These predictions are listed in the Monday blog post at Nate Silver's 538 blog.)

Here's a complete ranking of the polling companies from most accurate to least, according to a polysci professor who makes this comparison after each presidential election.

Rasmussen bombed in 2012, having predicted a 1-point edge for Governor Romney, but Rasmussen did quite well in 2008, calling the spread within 1.3 points, and earning the top ranking among the major polling films.

Gallup, on the other hand was one of the least accurate major polling companies in both the 2008 and 2012 presidential elections. In 2008, which they called +11 for Obama, the President won that election by 7.3, so Gallup was off by more than 3 points. In 2012 they called it +1 for Romney, so they again missed by more than 3. Neither result jibes with Gallup's margin of error, which is theoretically +-2 based on their sample size. Gallup was rated 17th out of 20 firms ranked in 2008, and 24th out of 28 firms ranked in 2012. The respected firm obviously needs to re-think some aspect of its methodology.

The most consistent performance in the past two elections was delivered by YouGov, which finished third both years.

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