538: Voters really did switch to Trump at the last minute

[pnwmom]

http://fivethirtyeight.com/features/voters-really-did-switch-to-trump-at-the-last-minute/?ex_cid=story-facebook

Donald Trump’s somewhat surprising win has forced many political analysts to wonder: Were we wrong all along in thinking Hillary Clinton had the upper hand, or was late-breaking movement to Trump part of the reason why polling averages missed his upset Electoral College victory? There’s certainly evidence that the polls underestimated Trump’s support in crucial Midwest states. But the latest wave of the Institute for the Study of Citizens and Politics panel survey that my University of Pennsylvania colleague Diana Mutz and I have been overseeing is now complete, and it provides new evidence that voters did shift to Trump in the final weeks of the campaign, too.

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At first glance, it might seem as if Clinton in October 2016 was in roughly the same position as Obama was in October 2012, at least with respect to the distribution of votes nationally: Both enjoyed margins of 7 percentage points among exactly the same group of people. But there were critical differences, even beyond the fact that the geographic distribution of support is crucial in making one candidate president. First, the number of undecided respondents in 2016 was 21 percent, significantly outpacing the 15 percent we saw in 2012. Second, our 2016 survey ended on Oct. 24, leaving two full weeks before the Nov. 8 election for people’s minds to change. There was still a lot of time on the clock.

And while most people’s support remained the same, the changes we did observe were consequential. Consider the table below, showing panelists’ support in the October 2016 poll versus their support in the post-election poll, which took place from Nov. 28 to Dec. 7. Eighty-nine percent of the 1,075 American adults reported the same preference in both waves, whether it was for Clinton (38.0 percent), Trump (35.2 percent) or neither (15.8 percent). But among those who did move, Trump had the advantage. While no one moved from Trump to Clinton, 0.9 percent of our respondents moved from Clinton to Trump. Although that 0.9 percent isn’t a lot, those changes are especially influential, since they simultaneously reduce Clinton’s tally and add to Trump’s. If there were a comparable swing in the national electorate, 1.2 million votes would move to Trump.

Trump also outpaced Clinton among people who were previously undecided or third-party backers, with 3.1 percent of respondents moving from those categories to Trump while just 2.3 percent did the same for Clinton. Clinton also saw 3.1 percent of her October supporters defecting to third-party candidates or becoming undecided. Trump lost just 1.7 percent.

In all, Trump picked up 4.0 percentage points among people who hadn’t been with him in mid-October, and shed just 1.7 percentage points for a net gain of 2.3 points. Clinton picked up a smaller fraction — 2.3 points — and shed 4.0 points for a net loss of 1.7 points. . . .

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