"The Polls Missed Trump. We Asked Pollsters Why.", 538

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"The Polls Missed Trump. We Asked Pollsters Why.", 538

Postby Natural ChemE on November 9th, 2016, 10:58 pm 

Yesterday (2016-11-08), the 2016 US presidential election concluded with expected underdog Donald Trump (positions) winning the Presidency, such that he'll be the 45th President of the United States.

There's some confusion about his victory because researchers expected Clinton to win. Data scientist Nate Silver had given Clinton 71.4% odds, vs. 28.6% for Trump. Some forecasters were even dismissive of Trump's chances, e.g. The Huffington Post gave Clinton 98.2% odds, which Silver had dismissed ahead of the election, warning that a Trump victory, while not the most likely outcome, was entirely possible.

Now contributors at FiveThirtyEight explain their perspective on the forecasts versus the election's outcome:
The Polls Missed Trump. We Asked Pollsters Why., Carl Bialik and Harry Enten via FiveThirtyEight (2016-11-09) wrote:The polls missed Donald Trump’s election. Individual polls missed, at the state level and nationally (though national polls weren’t far off). So did aggregated polls. So did poll-based forecasts such as ours. And so did exit polls.

The miss wasn’t unprecedented or even, these days, all that unusual. Polls have missed recent elections in the U.S. and abroad by margins at least as big. Every poll, and every prediction based on it, is probabilistic in nature: There’s always a chance the leader loses. And Clinton probably didn’t even lose the national popular vote; she just didn’t win it by as much as polls suggested. But Tuesday’s miss was an important one because Clinton appeared to lead by a margin small enough that it might just have been polling error. That turned out to be mostly true — true enough for her to lose in the Electoral College, and for Democrats to fall far short of taking control of the Senate.

It will take a while to figure out exactly why polls missed. Reviews by pollsters and their professional organizations can take months. “The polls were largely bad, including mine,” Patrick Murray, director of the Monmouth University Polling Institute, wrote us in an email. “But if anyone thinks they have the answer right now, they are just guessing.”

We wrote before the election that a polling error of 2 to 3 percentage points is normal these days. Before we dive into the details of what happened Tuesday, and why it happened, let’s step back and look at the different kinds of polling error. All of them are important because all of them were present in this result.

Every poll has error, some from statistical noise and some from factors more difficult to quantify, such as nonresponse bias.

[...more...]

This thread's meant to focus on arguments from FiveThirtyEight; for general discussion, please see the what causes errors in political polls? thread.
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Re: "The Polls Missed Trump. We Asked Pollsters Why.", 538

Postby TheVat on November 10th, 2016, 12:38 am 

538 seems spot on about the "shy Trump voter" effect, where they are reticent about disclosing their choice to a pollster. And, as as happened before, there's the tendency of Dems to blow off actually voting, even if they sound gung-ho early on. As I noted elsewhere, BHO got near 70 million in 2008, due to unusual mobilization pollward. HRC was under 60 million, even after 8 years when minority populations added several million. That Will Rogers quote remains fresh, 80 years later, "I am not a member of any organized political party: I'm a democrat!"
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Re: "The Polls Missed Trump. We Asked Pollsters Why.", 538

Postby mitchellmckain on November 11th, 2016, 6:36 am 

My guess/speculation is that the polls tend to be biased towards those who communicate more and it is the more non-communicative sector of the voters which favored Trump. It's not just the polls but in all the media which was thrown for a loop in this. I certainly didn't see it coming. I could even imagine people voting for that guy. But they did! I guess that we will be trying to figure out why for some time to come.
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Re: "The Polls Missed Trump. We Asked Pollsters Why.", 538

Postby mitchellmckain on November 12th, 2016, 12:57 am 

mitchellmckain » November 11th, 2016, 5:36 am wrote:My guess/speculation is that the polls tend to be biased towards those who communicate more and it is the more non-communicative sector of the voters which favored Trump. It's not just the polls but in all the media which was thrown for a loop in this. I certainly didn't see it coming. I could even imagine people voting for that guy. But they did! I guess that we will be trying to figure out why for some time to come.


Thanks to an observation by my eldest son, we can give this a flashy name. He made the observation that most forums and places on the internet have more silent observers than active participants. Thus we can call this "the lurker effect" when these silent observers are given a voice in something like a presidential election.
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