Election 2016: How Exit Polls Predict the Winner

Exit polls can provide a glimpse of who the next president will be well before the final votes are counted.

Tens of millions of Americans are heading to the polls today. Counting all of the votes takes hours and even days, but news organizations will call which presidential candidate won what state -- and eventually the election itself -- well before the last vote is tallied.

How is that possible? Exit polls.

Exit polls are surveys conducted by hundreds of interviewers across the country at a sampling of polling places. The interviewer approaches voters as soon as they leave the polling site, and asks who they chose and why. Exit polls aren't just a preview of how the vote might split; they also provide insight into why a particular candidate or party won on Election Day. Demographic data for each voter are also taken.

Not everyone votes in-person on Election Day of course. A third of the electorate in 2014 either voted early or by absentee ballot. That number will likely rise in this election. To reach these voters, telephones polls are also used.

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Although some demographic data dealing with voter turnout is released over the course of Election Day, final numbers showing who won a particular state are held under strict embargo until polls are closed. This secrecy is considered necessary to prevent survey data from influencing the outcome of the election. If a candidate's supporters think that he or she already won a particular state, the thinking goes, they may stay home, assuming that part of the race is already decided.

This year, however, there's a new twist on exit polls, as POLITICO'S Steven Shepard reports, with a handful of organizations promising live exit poll results with the aim of creating a real-time snapshot of where the election stands.

The embargoed exit polls used by news organizations are conducted by one firm. Since 2003, Edison Research, based out of Somerville, N.J., has been the traditional provider of exit poll data, responsible for the massive undertaking of conducting polling for the National Election Pool (NEP), a group of media organizations that includes the Associated Press, ABC, CBS, CNN, FOX News, and NBC.

One company, VoteCastr, has partnered with Slate and Vice to publish its own minute-by-minute polls throughout Election Day. "Our goal is not to beat the networks and wire services to declaring winners and losers -- election night will still belong to their analysts and their magic walls -- but to guarantee that citizens who have been entrusted with a vote also have access to as much information as possible about how their fellow citizens are voting," Sasha Issenberg, editorial director and chief strategist for VoteCastr, writes in a blog post explaining the purpose of the project.

"VoteCastr's technique is the same one campaigns use to track voter activity on Election Day, gathering information that they use to direct last-minute campaign resources, lobby voters, and prepare for the result to come," Slate editor Julia Turner writes in a separate piece explaining the need to break the traditional news Election Day embargo. "Making similar data available to our readers will help level the playing field."

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Given all of the attention to exit polls, how do we even know that they're accurate? In a blog post, Edison co-founder Joe Lenski details what goes into some of the logistics involved with producing exit polls data. This includes training interviewers extensively, avoiding biased or leading questions, guaranteeing a respondents' privacy, and ensuring transparency with exit poll methodology, among other measures.

No matter how scientifically rigorous the process for administering a poll, error will skew the results. And for that reason, unless exit poll data show a wide gulf between the candidates, news organizations make projections of winners in close races using a combination of pre-Election Day polls, exit poll data, vote returns as reported by election officials in certain precincts, and vote tallies at the county level, according to Edison. Furthermore pollsters will not visit every state, visiting only 28 states, down from 31 in 2012, for reasons of cost and competitiveness.

Early exit poll data from Edison the NEP and the will start to trickle out at around 5:45 p.m. today, with full results from a handful of states first available at 7:00 p.m. Eastern time. For anyone who simply can't wait that long, there's always VoteCastr to keep you updated throughout the day.

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