This is a plea to all of my friends on DKOS to not fall into the trap of living and dying by the purported exit poll results that are leaked throughout the day. Folks like Matt Drudge love to release numbers that simply are meaningless in terms of predicting the actual outcome. Remember four years ago? Many thought Kerry had it in the bag because of some exit poll numbers released. Whatever is released will never give an accurate picture of the final vote tallies.
Nate Silver released a primer:
- Exit polls have a much larger intrinsic margin for error than regular polls. This is because of what are known as cluster sampling techniques. Exit polls are not conducted at all precincts, but only at some fraction thereof. Although these precincts are selected at random and are supposed to be reflective of their states as a whole, this introduces another opportunity for error to occur (say, for instance, that a particular precinct has been canvassed especially heavily by one of the campaigns). This makes the margins for error somewhere between 50-90% higher than they would be for comparable telephone surveys.
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- "Leaked" exit poll results may not be the genuine article. Sometimes, sources like Matt Drudge and Jim Geraghty have gotten their hands on the actual exit polls collected by the network pools. At other times, they may be reporting data from "first-wave" exit polls, which contain extremely small sample sizes and are not calibrated for their demographics. And at other places on the Internet (though likely not from Gergahty and Drudge, who actually have reasonably good track records), you may see numbers that are completely fabricated.
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- A high-turnout election may make demographic weighting difficult. Just as regular, telephone polls are having difficulty this cycle estimating turnout demographics -- will younger voters and minorities show up in greater numbers? -- the same challenges await exit pollsters. Remember, an exit poll is not a definitive record of what happened at the polling place; it is at best a random sampling.
Go read it, or Mark Blumenthal's lengthier write-up.
It will not do us any favors to sit here and crow/freak out about exit polls before the vote counting actually begins.