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FiveThirtyEight

Politics

It’s Tuesday, November 4th, 2008, Election Day in America. The last polls have straggled in, and show little sign of mercy for John McCain. Barack Obama appears poised for a decisive electoral victory.

Our model projects that Obama will win all states won by John Kerry in 2004, in addition to Iowa, New Mexico, Colorado, Ohio, Virginia, Nevada, Florida and North Carolina, while narrowly losing Missouri and Indiana. These states total 353 electoral votes. Our official projection, which looks at these outcomes probabilistically — for instance, assigns North Carolina’s 15 electoral votes to Obama 59 percent of the time — comes up with an incrementally more conservative projection of 348.6 electoral votes.

We also project Obama to win the popular vote by 6.1 points; his lead is slightly larger than that in the polls now, but our model accounts for the fact that candidates with large leads in the polls typically underperform their numbers by a small margin on Election Day.

This race appears to have stabilized as of about the time of the second debate in Nashville, Tennessee on October 8th. Since that time, Obama has maintained a national lead of between 6 and 8 points, with little discernible momentum for either candidate. Just as noteworthy is the fact that the number of undecided voters is now very small, representing not much more than 2-3 percent of the electorate. Undecided voters who committed over the past several weeks appear to have broken roughly equally between the two candidates.

Our model forecasts a small third-party vote of between 1 and 2 points total; it is not likely to be a decisive factor in this election except perhaps in Montana, where Ron Paul is on the ballot and may garner 4-5 percent of the vote.

Any forecasting system is only as good as its inputs, and so if the polls are systematically wrong, our projection is subject to error as well. Nevertheless, even as we account for other cycles in which the polling numbers materially missed the national popular vote margin (such as in 1980), a McCain win appears highly unlikely. It is also possible, of course, that the polls are shy in Obama’s direction rather than McCain’s, in which case a double-digit win is possible.

Nor does McCain appear to have much chance of winning the Electoral College while losing the popular vote; in fact, our model thinks that Obama is slightly more likely to do so. McCain diverted many of his resources to Pennsylvania, a state where he narrowed Obama’s margins somewhat, but which our model concludes that Obama is now virtually certain to win. This may have allowed Obama to consolidate his margins in other battleground states, particularly Western states like Colorado and Nevada to which McCain has devoted little recent attention.

Thank you for placing your trust in FiveThirtyEight.com over the course of the past several months. We hope that you will join us both on the website and on HDNet tonight, where I’ll be providing election coverage for Dan Rather’s team. FiveThirtyEight intends to continue to apply our unique approach to politics after the election, and we hope to have several announcements about our future plans in the coming days and weeks.

*** One very quick technical note: I have removed the regression estimate from the final projection for the five states that are the home of either a presidential or vice presidential candidate (Arizona, Alaska, Illinois, Hawaii, Delaware); we have plenty of polling data to look at in these states and the regession model was having difficulty accounting for home-state effects.

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