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Exit Poll from WikiPedia:

An election exit poll is a poll of voters taken immediately after they have exited the polling stations. Unlike an opinion poll, which asks whom the voter plans to vote for or some similar formulation, an exit poll asks whom the voter actually voted for. A similar poll conducted before actual voters have voted is called an entrance poll. Pollsters – usually private companies working for newspapers or broadcasters – conduct exit polls to gain an early indication as to how an election has turned out, as in many elections the actual result may take hours or even days to count.

Warren Mitofsky, founder of Mitofsky International, is credited with having invented the exit poll.

Exit polls are also used to collect demographic data about voters and to find out why they voted as they did. Since actual votes are cast anonymously, polling is the only way of collecting this information.

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