Wednesday, November 16, 2016

Follow-Up On Polls, Probability, and the Election

About a week ago, I blogged my thoughts on what happened with the election polls, which made it look like Clinton would win the election. One explanation I had was social desirability bias:
Finally, we have the possibility that people did not respond the way they actually feel to the poll. This usually happens because of the influence of social desirability. People want to be liked, and they want to answer a question the way they feel the interviewer wants the question to be answered.

People often hold public attitudes that differ very much from their private attitudes. This occurs when they think their private attitude is undesirable and differs from the majority (a concept known as pluralistic ignorance), so they insist they believe the opposite to feel a sense of belonging in the group. In fact, they may become very vocal about their public attitude, to overcompensate and try to prevent people from figuring that their private attitude is completely different.

What this means is, people may have said they were voting for Clinton publicly, but knew they would be voting for Trump privately.
Apparently, this explanation has been offered by many (unsurprising, since it's always a concern in surveying, particularly when dealing with sensitive issues). So many that it has become known as the "shy Trump" phenomenon. But some new analyses over at FiveThirtyEight offers some pretty compelling results to suggest that explanation is incorrect:
So if the theory is right, we would have expected to see Trump outperform his polls the most in places where he is least popular — and where the stigma against admitting support for Trump would presumably be greatest. (That stigma wouldn’t carry over to the voting booth itself, however, so it would suppress Trump’s polling numbers but not his actual results.) But actual election results indicate that the opposite happened: Trump outperformed his polls by the greatest margin in red states, where he was quite popular.

The second reason to be skeptical of the “shy” theory is that Republican Senate candidates outperformed their polls too.

Third, Trump didn’t outperform his polls with the specific group of voters who research showed were most likely to hide their support for his candidacy.

Finally, Trump’s own pollsters told us that there weren’t many shy Trump voters by Election Day. A few months before the election, internal polling showed Trump getting about 3 percentage points more support in polls conducted online or by automated voice recording than in live calls, according to David Wilkinson, data scientist for Cambridge Analytica, a data-analytics firm that conducted polling for the campaign. That suggests some Trump supporters were reluctant to reveal their true preference to a telephone interviewer. But in polls conducted just before Election Day, that 3-point gap had narrowed to just 1 or 2 points.
Full details and pretty figures at the link above. I maintain my argument that Trump is one of the most divisive candidates in history, and will likely go on to be the most divisive president in history. Though as a citizen I'm terrified, as a statistician, I can't wait to take a look at approval rating data. If Trump doesn't deliver on some of his big campaign promises (e.g., the dumb-ass wall idea), he'll piss off his base. And some of his choices for staff have angered both Democrats and mainstream Republicans. At the end of it all, is anyone going to like this guy?

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