Nonetheless, even if the models didn’t get things quite right, it was almost certainly correct to say that history gave the Patriots long odds. We can be confident about this because of the basic gut-check that I described before: There have been lots of NFL games, and comebacks like the one the Patriots made have been very rare. For example, according to the Pro-Football-Reference.com Play Index, there have been 364 games since 1999 (not counting Super Bowl LI) in which a team trailed by between 24 and 27 points at some point in the third quarter. (The Patriots trailed by 25.) Of those, the trailing team came back to win in only three games, or 0.8 percent of the time. There are various aggravating and mitigating factors you’d want to consider for Super Bowl LI — like that the Patriots had Tom Freakin’ Brady — so I’d guess that those models had New England’s chances too low. Even so, the Pats’ comeback required near-perfect execution, as well as some uncanny luck.
But for the election? That empirical gut-check you can often use for sports — that we’ve been in this situation hundreds or thousands of times before and that we know from history that it almost always turns out a certain way — doesn’t really work. For one thing, there’s not much data. Presidential elections are rare things; FiveThirtyEight’s model was based on only 11 previous elections (since 1972), and others were based on as few as five elections (since 1996). Furthermore, despite the small sample size, there were a fair number of precedents for a modest polling error that would nonetheless be large enough to put Trump into the White House. (In the end, Trump beat his polls by only 2 to 3 points in the average swing state, but that was enough to win the Electoral College). That’s why we thought it was sort of nuts to give Trump less than a 1 percent chance or a 2 percent chance on election morning, where some other models had him. Those were less empirically driven probabilities than adventurous extrapolations drawn from thin data.2
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