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Actually, the screen for likely voters (in a general election) is typical just "How likely are you to vote" (only asking people who are already registered). Many firms use an additional screen for "definite voters", which may rely on past voting history, etc, but this is almost never used/reported by the media. And of course, there are various things that pollsters do to weight survey respondents by likelihood to vote, etc, but again, the polls you see in the media are usually not that sophisticated.
People do overstate their intentions, as you say, so the screen for "likely voters" used by most polling firms nets the vast majority of people who end up voting. It is much more probable that a "likely voter" will end up
not voting than than that an "unlikely voter" will vote.
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Check out the Gallup standards from 2004:
http://www.mysterypollster.com/main/...oters_i_1.html
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Although Gallup has made minor modifications, the questions and procedures that Perry described 44 years ago remain in use by the Gallup Poll today. Among those who say they are registered to vote (or who plan to do so before the election), Gallup uses the following questions to create a scale that varies from 0 to 7:
1) How much have you thought about the upcoming elections for president, quite a lot or only a little? (Quite a lot = 1 point)
2) Do you happen to know where people who live in your neighborhood go to vote? (Yes = 1 point)
3) Have you ever voted in your precinct or election district? (Yes = 1 point)
4) How often would you say you vote, always, nearly always, part of the time or seldom (Always or nearly always = 1 point)
5) Do you plan to vote in the presidential election this November? (Yes = 1 point)
6) In the last presidential election, did you vote for Al Gore or George Bush, or did things come up to keep you from voting?" (Voted = 1 point)
7) If "1" represents someone who will definitely not vote and "10" represents someone who definitely will vote, where on this scale would you place yourself?
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New York Times says that places use past voting habits, length of residency registrations status, etc.
http://www.nytimes.com/packages/pdf/...gstandards.pdf