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Report: 2016 Polls Missed Key Factors

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President Donald Trump's victory over Hillary Clinton in the 2016 presidential election is still being analyzed months later, and a new report seeks to provide more context to the unexpected result.

Going into Election Day, nearly every major poll said it was a certainly that Clinton would easily win the race. According to the American Association for Public Opinion Research, those polls were mostly correct, given that Clinton won the popular vote by nearly 3 million voters.

However, the polls published in newspapers and online news sites missed several key factors that masked Trump's edge over Clinton among blue-collar voters, especially in the three states she unexpectedly lost in: Michigan, Wisconsin and Pennsylvania. Together, those states' 46 electoral votes would have been enough to tip the election to Clinton.

The AAPOR said there are three reasons polls underestimated Trump.

One reason was that many voters waited until the final week to make their decision, including about 13 percent of voters in Wisconsin, Pennsylvania, and Florida -- all of which went to Trump. Those last-second deciders overwhelmingly sided with Trump. In Wisconsin, Trump had a whopping 30-point edge over Clinton in that category of voters; in Pennsylvania and Florida, those voters picked Trump by 17 percent.

The second reason was a lack of polling among non-college graduates. Not many polls bothered surveying people who did not have a college degree, according to the AAPOR. There was a strong correlation between education level and voter preference, with Trump tending to beat Clinton among those without a college degree. But because those voters were largely ignored, Trump's overall level of support was missed by the polls.

The third reason was that many Trump supporters were not upfront about their support for the controversial billionaire until after the election.

The AAPOR also said that Trump's name appearing first on the ballot in many states contributed to his win:

State election rules led to Trump’s name appearing above Clinton’s on all ballots in several key states that Trump won narrowly (Michigan, Wisconsin and Florida). Being listed first can advantage a Presidential candidate by roughly one-third of one percentage point. Given that pollsters tend to randomize the order of candidate names across respondents rather than replicate how they are presented in the respondent’s state, this could explain a small fraction of the under-estimation of support for Trump, but ballot order represents at best only a minor reason for polling problems.

Another major factor was that Clinton did not make one campaign appearance in Wisconsin during the entire general election campaign. In addition, the Clinton campaign headquarters largely ignored Michigan, despite pleas from on-the-ground staffers for more resources, according to Politico.

"It takes a lot of work to lose to Donald Trump," said David Axelrod, the former senior adviser to President Barack Obama, according to CNN.

Sources: AAPOR, Politico, CNN/ Photo Credit: Gage Skidmore/Flickr

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