Page last updated at 19:15 GMT, Monday, 3 November 2008

Q&A: How US results are reported

American voters in San Diego cast their ballots
American voters in San Diego cast their ballots
How will the BBC report the results of the US election? This guide explains where the results come from, what exit polls are, and how states are called.

What is the source for the BBC's election results?

The Associated Press is providing the election result data for BBC News.

The AP is the sole organisation responsible for providing the results for the major American media networks. The information they provide will form the basis for election results but different broadcasters may decide to interpret partial results in different ways.

The BBC will report state results based on AP and one other major US media network, or our close partners ABC News alone.

How do the results take shape and what are "projected results"?

Initially the outcome of the US election is likely to be a "projection", based on exit polls and/or partial results. This means the result will be labelled as projected until all the votes are counted.

The reason for this is that states are often called, or declared, for a candidate, on the basis of incomplete figures. The American electoral system enables each state to release partial results to the public well before they have counted every single vote. Results are later confirmed once all the votes have come in.

For races that are not very close the US networks are likely to project a winner as soon as the polls close, based on exit poll data. For closer races the US networks will wait until there's more actual vote data. It can take hours or even all night.

If a projection is not immediate, it doesn't mean it is 'too close to call', rather it may simply be 'too early to call' because the networks have insufficient data.

Are the projections ever wrong?

Yes, particularly if the election is very close. Most memorably the major US networks, including Fox, CNN, NBC, CBS, and ABC gave Florida to Al Gore in 2000, only to retract that and then give it to George W Bush, and then to retract that while the result was under dispute.

What is an exit poll?

Exit polls are gathered by speaking to members of the public after they have voted. They are used in two main ways.

They can help predict the outcome of an election before all the votes are counted and they may also include information on demographics. For example, they could show which candidate appealed most to women voters, or who got the most support from the Hispanic community.

This year exit polls are being handled solely by Edison Media Research and Mitofsky International.

The BBC does not have access to the detailed exit poll data.

Is Washington DC a state?

No. DC, or the District of Columbia, is not a state, but it does receive three electoral college votes. DC is able to vote for president but it does not have senators or congressmen of its own.

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