Nate Silver says media assumptions, not data, led to surprise over 2016 election results

Christina Pazzanese in the Harvard Gazette:

GAZETTE: At last year’s conference here, you were still skeptical of Trump’s viability as the Republican Party nominee, which was fairly late. On election night, your site had Hillary’s chances at 71 percent; almost everyone else had her up by even more. Why do you think Trump’s victory blindsided so many?

SILVER: I think people shouldn’t have been so surprised. Clinton was the favorite, but the polls showed, in our view, particularly at the end, a highly competitive race in the Electoral College. We had him with a 30 percent chance, and that’s a pretty likely occurrence. Why did people think it was much less than that? I think there are a few things. One is that I don’t think people have a good intuitive sense for how to translate polls to probabilities. In theory, that’s the benefit of a model. But I think people thought “Well, Clinton’s ahead in most of the polls in most states, and I remember that seems similar to Obama four years ago, and therefore I’m very confident that she’ll win.” It’s ad hoc and not really very rigorous, that thought process.

The second part is that there is a certain amount of groupthink. People looking at the polls are mostly in newsrooms in Washington and Boston and New York. These are liberal cities, and so people tend to see evidence (in our view, it was kind of conflicting polling data) as pointing toward a certain thing.

More here.