Trump knew it, Hillary blew it — the failures of polling

Election season has come and gone. Donald Trump pulled off what has been repeatedly characterized as a “stunning upset” over bitter rival Hillary Clinton. The web has gone rampant with postmortem analysis about the failures of election polling. But was it really that stunning?

Several polls conducted in the lead up to the election reported on the virtually deadlocked race, all well-within any reasonable margin of error:

Quinnipiac University reported on the situation in key battleground states (Nov 2)

Democrat Hillary Clinton’s October momentum comes to a halt as she clings to a small lead in Pennsylvania, while Republican Donald Trump moves ahead in Ohio, leaving Florida and North Carolina too close to call.

Probability forecast models on the other hand were remarkably off-mark and predicted Clinton well-ahead just the night before the election:

  • New York Times Upshot: Clinton 84%, Trump 16%
  • FiveThirtyEight: Clinton 66.9%, Trump 33%
  • PredictWise: Clinton 89%, Trump 11%

I was watching the blitz of last-ditch rallies held by Trump and Clinton the night before election day, to learn about the sentiments they were expressing about their chances. Here is a revealing segment from Trump’s penultimate war cry in New Hampshire (8pm on Nov 7):

We are going right after this to Michigan, because Michigan is in play… The polls just came out: we are leading in Michigan; we are leading in New Hampshire; we are leading in Ohio; we are leading in Iowa; leading in North Carolina; I think we are doing really, really well in Pennsylvania; and I do believe we are leading in Florida.

In the meantime, according to the New York Times:

Mrs. Clinton’s campaign was so confident in her victory that her aides popped open Champagne on the campaign plane early Tuesday.

Either way, each candidate and their popular base was clearly happy to live in their own reality right up to the wire. Some personal take-aways from this whole affair:

  • Polling and forecasting is a messy, complex, empirical problem which next-to-nobody understands. I doubt it is statistical.

  • Well-informed voters do not derive the bulk of their information from cursory reading of social or national news media. They are vigilant about critiquing every aspect of information they consume. Otherwise, they are very, very sad.

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