CNN’s Decision Desk projects the winners of dozens of elections each year, ensuring that the network reports the outcome of major contests as soon as it is statistically sound to do so, using a combination of exit or entrance poll results, vote returns and statistical modeling.
Here’s a look at how CNN reports on the results of elections and how the CNN Decision Desk projects the winner.
Q. Where does CNN get its election data and information?
A. CNN is a member of the National Election Pool along with ABC News, CBS News and NBC News, working with Edison Research to collect vote returns from election officials and to conduct exit or entrance polls among voters who are casting ballots in major elections. Edison Research deploys a team of hundreds of interviewers and vote reporters across each state in those contests to conduct scientific surveys on voters’ opinions and to work with election officials to report election results quickly and accurately.
CNN correspondents and anchors are also often on the scene of major contests, reporting on what they learn about the situation on the ground from election officials and voters themselves, and can provide pieces of information about the vote count that are essential to accurate projections.
Q. How does CNN project races where one candidate holds a wide lead?
A. In some cases, CNN’s Decision Desk can project a result based on exit or entrance poll results when one candidate holds a very wide lead. Exit and entrance polls are effective for this purpose for several reasons.
First, a statistically sound sample can produce an accurate estimate of the outcome of the election within the poll’s margin of sampling error. In races with a wide margin, the difference between the two candidates vastly exceeds the error margin, giving the team confidence that the poll’s result will hold up when all the votes are counted.
Second, unlike pre-election polls, exit and entrance polls interview voters and caucusgoers at their polling places, eliminating the need for what pollsters call likely voter modeling, used to try to determine who will vote. Those conducting the poll can be sure that the people in these samples actually voted because they have physically shown up at the location where voting happens.
And finally, in states with large absentee or early voting populations, the National Election Pool will supplement results from in-person exit or entrance polls on Election Day with surveys of absentee and early voters conducted online, by phone or in-person to make sure that the views of all voters are reflected in those surveys.
Q. What about races with tighter margins?
A. Elections that cannot be projected based on exit poll results could ultimately be projected based on several different ways of analyzing actual vote data.
As vote returns start to come in, the CNN Decision Desk will be looking for patterns in the data, how the results and turnout compare with past results for each location, and whether there are any anomalies in what’s been reported so far.
As counties and localities begin reporting results, the team’s statistical models will start to run, modeling outcomes based on different combinations of past vote, type of vote and geographic region. Consistent, strong models using those data and producing a high level of statistical confidence (99% certainty or more) could lead to a projection of the winner.
At the same time, Edison Research will attempt to collect the actual vote at each of the places where an exit poll was conducted, and since that sample of voting locations is a scientifically representative sample of all locations in a state, it is possible that those vote results could be enough to make for a statistically sound projection, even if there isn’t much county-level vote reported.
And in the closest races, the CNN Decision Desk will be looking closely at estimates of how much vote is left to count – overall amount, what type it is and where it could come from. Determining whether there is enough remaining vote to shift the outcome will be the central question in deciding when it is possible to project a winner.
