NBC News is a member of the National Election Pool, a consortium formed by NBC, ABC, CBS and CNN. The NEP consortium, along with Edison Research, conducts exit and absentee polls, provides precinct votes in selected sample precincts and runs models for the analysis of the election information. The NEP also delivers statewide vote counts, as well as county by county results, for general elections and district votes in House races.

NBC News election unit analysts will first examine exit polls, any absentee polls and statistical estimates based upon this data in a given race to determine if the race can be called. As election night goes on, analysts also examine vote results from selected sample precincts, county-by-county model results, the actual raw votes (both statewide and county by county) and additional statistical information. In order to make a race call, all senior election unit analysts must agree, the NBC News director of elections must agree and the senior news division management representative must agree. If everyone agrees, a call is made.

NBC News will not project a winner in a race until after the last scheduled poll closing time in that race. If the race appears to be close in any state, an abundance of caution will be used before calling a race in that state.

The large number of absentee and early voting has required that our election projection methods ensure that absentee voters are properly accounted for. Absentee ballot polls and analysis of early-voting data will be conducted when appropriate and statistical models account for this trend.

The director of NBC News' decision desk, the decision analysts and the quality-control desk operate independently from NBC News editorial teams and outside election reporting.

Understanding election night calls

NBC News will be clear about its nomenclature during the entire election process. In addition, NBC News will explain methodology for collecting data it presents. Here are some terms you will hear on NBC and MSNBC and read on NBCNews.com on election night:

Projected winner: NBC has made a projection that a candidate will win the race, but the vote count is not complete. This call is made only after all the polls are scheduled to have closed in that race.

Apparent winner: NBC has tallied enough votes to indicate that a candidate has won the race, but the results may well depend upon a potential recount or final official tallies.

Winner: A candidate who has clearly won the race, beyond the normal margin for a recount. "Winner" will not be used unless returns make the outcome a virtual certainty.

Note that none of these terms refers to the "official" winner, since most states take weeks to officially certify a winner in an election.

Too early to call: There is not enough data to allow analysts to make a call.

Too close to call: While there is data on the race, the numbers are too close to allow analysts to make a call.

Senate Composition: The Decision Desk tracks individual Senate races. This is not a projection of the entire Senate but reported results “at this hour” as individual races are called. The composition will show the totals in the new Senate by party, showing the new called races added in with seats that are not up for re-election this year.

House Estimate: This is a projection of the House as a whole. For each of the 435 individual House races, the Decision Desk calculates the probability of a Democratic, Republican or independent victory in that House seat, based on pre-election research. During the night, election analysts examine all the available vote data and adjust the probabilities for each House seat that changes from its pre-election probability. The model then calculates the most probable outcome of the election in the House and also calculates an estimate of the probability of error expressed as a number of seats plus or minus. Based on the House Estimate, there is also a probability of a certain party winning control of the House.

In addition, individual House calls are made and tracked throughout the night. Like the Senate composition, the individual House races will be tallied as races are called and may not add to 435 called races on election night.

Understanding results on NBCNews.com

NBCNews.com.com receives data from the NEP, which gathers three sets of data on Election Day: 1) Exit polls, conducted by the NEP 2) Projection information that is used by NBC to "call," or project, a race once all the polls have closed 3) Unofficial vote tallies, as reported by election officials.

For exit polls, voters leaving the polling place in selected voting districts are handed a questionnaire with both demographic (sex, race, age) and attitudinal questions (Do you approve or disapprove of the way Congress is handling its job?). They are also asked to indicate how they voted. Those responses are collected and then transmitted to the NEP, so the results are tabulated and reported.

NBC News, along with the NEP, is conducting exit polls of voters as they exit their polling place on Election Day. This is the only in-person poll on Election Day. The data is valuable because its a true measure of voters. We know that the respondents have just voted because they exit their polling place and are handed a survey.

The in-person exit poll is also supplemented with a telephone poll in states with high absentee and early voting to get an accurate picture of who voters are and what motivated them to vote on Election Day.

For vote tallies, results are gathered from election officials in each state as the vote is reported. These are "unofficial" returns because the tallies have not been rechecked and certified by state election authorities.