538 gave Clinton an 86% chance for a brief period of time after the Access Hollywood tapes but before Comey's press conference. I wouldn't call that a lock, but maybe some would.

86% is about a one in seven chance of not happening. It's very much not what anyone would treat as a lock on anything that had important consequences.

I grant you plenty of people have sufficient trouble understanding probabilities that they would mistake 86% for a lock, though.

Yeah, and then nobody bothered to watch as her chances drifted downward every subsequent day until the election... and they drifted down because the polls changed and the model got more information. It's not really fair to say the model was wrong- it just wasn't clairvoyant.

Really, Trump won by a hair's breadth. 538 shouldn't have given him a huge chance to win- he just barely scraped through. It's a genuinely hard problem when the popular vote is very close, since the electoral college throws a huge chaos wrench into everything.,

What should the number have been, then? The final results were essentially a tie with Trump winning the tie breaking coin toss. So 50/50 is right in hind sight. Te systemic error could just have been as easily in Clinton's favour as Trump's, so the number should have been smaller than 50% for Trump. Maybe not as small as 28%, but they weren't far off, IMO.

The model predicts a chance of winning, it doesn’t reflect the final vote percentages. In other words, a win is a win, regardless of whether it’s by a few votes or a landslide. That’s what the 80/20 represented. This is different than the polling averages. Though, electoral vote percentages are captured in 538’s model — they show a spread of possible win scenarios based on many numbers of runs of the model.

One could imagine such a non-linear model, but one wouldn't consider it well-behaved or even particularly useful for aiding one's understanding of reality.

The votes coming down to a dead heat doesn't mean that, the day before, they were equally likely to win. Suppose there were 100 possible futures. In 90 of them, Alice wins, by a little or a lot. In 8 of them, Bob barely wins, and in 2, Bob wins comfortably. Maybe this is determined by rigged dice or something, to make it strictly mechanical: there's 100 possibilities, and we know what they are and how they're distributed.

Just because you end up in the 9/100 future doesn't mean that the "real" probability was 50%. It's weak evidence that Bob's win scenarios mostly didn't involve blowouts.

It's like barely winning a sprint against Usain Bolt: maybe he had an injury midway through. Doesn't mean that he and I were equally likely to win.

The "score" was 1,405,280 to 1,382,536. That was the count in Wisconsin. Looks like a virtual tie to me.

That's the information we have, and it's real, so it's much more valid than any poll which poorly samples a few thousand people.

Maybe it was a fluke result. But that's unlikely because the other Midwestern states had similar results. But a fluke in which direction? You don't know, so it's even odds in both directions.

Perhaps people read 538's odds numbers as poll numbers.