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How does CNN make election projections?

(CNN) -- To project an election, CNN and its election experts use scientific statistical procedures to make estimates and calculate the odds of being right or wrong. When the experts think it safe, CNN then broadcasts a projected winner.

CNN editorial policy strictly prohibits reporting winners or characterizing the outcome of a contest in any state before all the polls are scheduled to close in every precinct in that state.

For the 2002 elections CNN will be receiving information from the following three sources:

Voter News Service: Along with the broadcast networks and the Associated Press, CNN is a member of a "pool" called Voter News Service (VNS). During elections, VNS tabulates the popular vote. VNS also conducts exit polls at the national level and for many statewide contests. The exit polls ask voters their opinion on a variety of relevant issues, determine how they voted, and ask a number of demographic questions to allow analysis of voting patterns by group.

Using the exit polls results and a number of sophisticated analysis techniques, VNS also projects winner for each race it covers. CNN will not use exit polls to make projections in close races. CNN will only use exit poll survey data to project a winner when that data indicates one of the candidates has a significant lead at the time that the polls close in that state.

CNN RealVote: In 10 key states Tuesday, CNN will collect information from randomly chosen precincts, which will be used to help project the winner in those states. CNN will refer to these as RealVote states during the evening.

After the 2000 elections CNN made a commitment to have a second source for data to make projections. The RealVote system will indicate where CNN is using that second-source information.

To assist CNN in collecting and evaluating this information, CNN has employed Mitofsky International and Edison Media Research. In previous elections, Warren Mitofsky and Joe Lenski have also assisted CNN in projecting winners in state and national races.

CNN may use the RealVote system to make a projection before VNS makes a projection in the same race. CNN may also choose not to air a projection made by VNS if the statistical analysis indicates the VNS projection does not meet the new criteria CNN has put in place for this election.

The Associated Press: This year CNN will receive vote totals from The Associated Press as a backup to the VNS system. AP will provide statewide vote totals for each race as well as vote totals in each county. If there is a problem with the VNS system, CNN will switch to use material from the AP.

Collecting data

The process of projecting races begins by creating a sample of precincts in each state. The precincts are selected by random chance, like a lottery, and every precinct in the state has an equal chance to be in the sample. They are not bellwether precincts or "key" precincts. Each one does not mirror the vote in the state but the sample collectively does.

The first indication of the vote comes from the exit polls conducted by VNS. On Election Day, VNS interviewers stand outside of hundreds of sample precincts across the country. They count the people coming out after they have voted and are instructed to interview every third person or every fifth person, for example, throughout the voting day. The rate of selection depends on the number of voters expected at the polling place that day. They do this from the time the poll opens until shortly before it closes.

The interviewers give each selected voter a questionnaire, which takes only a minute or two to complete it. It asks about issues that are important, and background characteristics of the voter, and it also asks for whom they voted in the most important races. During the day, the interviewer phones the information from the questionnaires to a computer center. CNN has its first estimate of an election result shortly after those phone calls come in.

Next, vote returns come in from the same sample precincts as the exit poll after the voting has finished in those precincts. These are actual votes that are available after the polls have closed and the precinct officials have counted the votes in that precinct. The results are posted so anyone at the precinct can know them. VNS will have a reporter at each sample precinct and they also phone the results to the computer center where estimates are made.

CNN has its own system to collect actual votes from its own separate samples of precincts in 10 states with close races. CNN is not conducting exit polls in these states. These separate CNN samples and computations will allow us to confirm the results that we are receiving from VNS so that we can be confident in our projections. In the rare cases where CNN samples and computations do not agree with the VNS computations, CNN's analysts will be even more cautious in our projections.

The third set of vote returns come from the vote tallies done by county officials in every state. (In the six New England states, cities and townships instead of counties do vote tallies.) The countywide figures become more complete as more precincts report vote returns. Late at night, all precincts have reported in most counties. This may or may not include the absentee vote. In some states the absentee vote is counted immediately on election night; in other states the absentee votes are included a day or more later. The county vote is put into statistical models and estimates and projections are made. This will be done by VNS. The Associated Press collects the county vote as well. VNS and the AP reporting of the county vote will be compared throughout the night to make sure most vote tally errors are caught.

Projections

CNN will decide on when and how to make a projection for a race depending on how close the race is.

In races that do not appear to be very close, projections may be made at poll closing time based entirely on exit poll results, which are the only information available when the polls close about how people voted. The races projected from exit polls alone are races with comfortable margins between the top two candidates. Projections from exit poll will only be made if they are consistent with pre-election polls. The victory margins for an exit poll projection are typically eight percentage points or more. If the race is closer than that, CNN will wait for actual votes to be tabulated and reported. VNS will make these projections and CNN will monitor them. If they don't meet the more rigorous criteria set up by CNN after the 2000 election, CNN will withhold those projections.

The margin would typically be eights points or more for an exit poll projection but projections depend on the margin of error and the size of the lead between the candidates. The margin of error calculation is part of the model. VNS will make a projection when there is a smaller lead than CNN requires. That is one reason why VNS may sometimes make a projection that CNN will not broadcast immediately.

Shortly after poll closing time, VNS will try to make projections using models that combine exit polls and actual votes. This can sometimes be useful for closer races, perhaps as close as four percentage points. But after poll closings, CNN analysts will rely only on actual votes. CNN has its own samples for key races and will use them along with those VNS estimates that are based only on actual votes. The projections again will be made when the margin of error is small enough for the projection to be safe. The odds of making a wrong projection will be less than one chance in 100.

For extremely close races, CNN will rely on actual votes collected at the county level. These are the races that cannot be projected at poll closing from exit polls or even from actual votes collected at the sample precincts mentioned earlier. The projection will be based on a statistical model that uses the county votes. If it is too close for this model to give us a reliable projection, CNN will wait for election officials to tally all or almost the entire vote.

Finally, there are races that CNN will not project on election night. CNN will not make a projection if it looks like the final winning margin is less than one percentage point. That is because the unofficial election night vote tallies in the past have on occasion had errors that are almost that large. Instead, CNN will make it clear that one candidate is ahead and that announcing a winner will depend on an official verification of the vote.

What a projection call means

CNN Decision Desk analysts will review all projections from VNS before they are accepted by CNN. CNN's team of analysts also will make its own projections. When CNN's analysts project a winner in a race, whether it is based upon data from VNS or from the CNN computations, it means that when all the votes are counted, CNN projects that the candidate will win the election. The projection from the analysts is as close to a statistical certainty as seems necessary to avoid any mistakes. That does not mean that a mistake cannot happen, but every precaution has been taken to see that it does not. CNN will not "declare" someone a winner because that is up to election officials. We will make projections based on our best estimate of how CNN expects the election to turn out.

When a lot of vote returns have been tallied, a race may be referred to by CNN anchors and analysts as "too close to call." "Too Close to Call" means the final result will be very close and that the CNN Decision Desk may not know who won. CNN will not say a race is "too close to call" early in the night because CNN doesn't have enough vote returns to say someone has won. In that case CNN anchors and analysts will instead say something like "we don't have enough information to know how the race is going," because when the votes come in the winner may, in fact, have a comfortable margin.


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