Must-Read: The fact that Nate Silver and http://fivethirtyeight.com choose to express their forecast as a pseudo-Bayesian win probability and relies on an underlying model in which uncertainty is necessarily symmetric has, I think, substantially impeded communication about the state of the presidential election. So let me endorse this attempt by Matthew Yglesias to bring clarity:
Matthew Yglesias: Nate Silver’s model underrates Clinton’s odds: "Even if you buy Silver’s main modeling assumptions (and I largely do)...
...there’s considerable evidence outside the realm of things captured by poll aggregators that leads me to believe that if the polls are wrong, they are more likely to be underestimating Clinton’s support than overstating it....
If someone offers you 2-1 odds on an election bet, you should probably take the Clinton side of the wager. Clinton is ahead in the polls.... I’m not pointing to them to say that the polls are wrong. I’m just saying that if they are wrong, it’s unlikely that they are wrong in a way that favors Trump.
The uncertainty is one-sided.... Silver sees a race with high variability and a high degree of uncertainty... the high number of people telling pollsters they will vote for Gary Johnson, for Jill Stein, or that they are still undecided.. His logic, which seems very correct to me, is that a 44-41 lead is a lot less safe than a 51-48 lead.... But while there really is a lot of uncertainty... it’s wrong to think of that as symmetrical uncertainty.... Johnson’s own vice presidential candidate, former Massachusetts Gov. Bill Weld, has also made his preference for Clinton clear. Johnson’s voters also skew very young, which is a terrible demographic for Republicans in general and for Trump in particular.... Of the four possible things a Johnson/Stein voter could do on Election Day--stick to his guns, defect to Clinton, stay home, or defect to Trump--the fourth option is a lot less likely than the other three....
Barack Obama’s strong approval ratings over the past two months are another reason to believe that uncertainty in the election is not symmetrical.... The fact that most people approve of the job President Obama is doing, and that his net margin on this score is a healthy 6 percentage points, however, gives us some clues to their overall thinking.... [For] a voter who likes Obama but is undecided because he doesn’t like Clinton... casting a ballot for the most virulently anti-Obama candidate in the race is the least-likely outcome. Early voting has good news for Democrats. Nevada... Florida....
It’s not a mistake that poll-based models don't include things that aren't polls. But one of the nice things about not being a professional poll-based forecaster is you are free to consider nonpoll information. The geography of Clinton’s pattern of support gives her an Electoral College disadvantage.... But if you spot her Nevada’s six electoral votes, that disadvantage goes away. The Florida situation is a lot less clear. But it's an absolute must-win state for Trump and not for Clinton.... Last, but by no means least, by essentially all accounts Clinton has a significant edge in the “ground game”.... Obama had the edge over Romney on this score in 2012, and Clinton is operating with significant continuity with what Obama began. But Clinton also has a significant cash advantage over Trump, which Obama lacked....
Trump is probably going to lose. Clinton is probably going to win. Nothing is certain in life until it happens, but her odds are a healthy margin better than two-to-one.
