Where does the BBC source its election results?
The Associated Press is providing the election results published on the BBC News website.
AP is the key organisation responsible for providing the results for the major American media networks. The information AP provides is likely to form the basis for most election results but different broadcasters may decide to use it in different ways.
This is because, in American elections, running tallies of the latest results in each race are made public while counting is still under way, creating the opportunity for partial results to be interpreted differently by different organisations.
The BBC has a relationship with US network ABC, and may take into account their decisions on races, as well as those of AP.
What does "calling" mean?
Calling a state, or calling the whole election, is the process whereby candidates are declared winners by different broadcasters ahead of the final votes being counted.
WHAT'S UP FOR GRABS?
All 435 seats in the House of Representatives
Thirty-three seats in the Senate
Thirty-six state governors
Decisions on calling are made by individual broadcasters when they believe they have enough information, either from exit polls or from the votes counted, or both, to be able to make a decision and declare a winner.
Are the calls ever wrong?
Yes. This is most likely to happen if the election is very close. Most memorably several major networks called Florida for Al Gore in the presidential election of 2000, only to issue a retraction and then call it for George Bush, and then to retract that while the result was under dispute.
What is an exit poll?
As in 2004, this year's exit polls are being handled by Edison Media Research and Mitofsky International.
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.