Mark Blumenthal | February 5, 2008
Topics: 2008 , Exit Polls
Looking for leaked exit poll results from the Super Tuesday states? As regular readers know, the leaks of exit poll we experienced in 2004 and prior years have been stopped, as the the network consortium that conducts the exit polls now restricts access to a small number of analysts in a "quarantine room" for most of the day and did not release the results to the networks and subscriber news organizations until 5:00 p.m. eastern time. While some of that information will leak a leak, that process will remain in place today (Tom Webster, an employee of Edison Research, has blogged some details about life inside the quarantine room).
What this means (and those of you who play the various election "futures" or predictions markets should listen closely) is that any "exit poll" numbers you hear about before 5:00 p.m. are bogus (or at least, not produced by the networks).
Here are a few tips for making sense of the exit poll data you will see tonight (a slightly edited version of tips I posted on the morning of the New Hampshire primary, with a few edits):
1) An exit poll is just a survey. Like other surveys, it is subject to random sampling error and, as those who follow exit polls now understand, occasional problems with non-response bias. In New Hampshire (in 1992) and Arizona (in 1996)* primary election exit polls overstated support for Patrick Buchanan, probably because his more enthusiastic supporters were more willing to be interviewed (and for those tempted to hit he comment button, yes, I know that some believe those past errors suggest massive vote fraud -- I have written about that subject at great length).
2) The networks rarely "call" an election on exit poll results alone. The decision desk analysts require a very high degree of statistical confidence (at least 99.5%) before they will consider calling a winner (the ordinary "margin of error" on pre-election polls typically uses a 95% confidence level). They will also wait for actual results if the exit poll is very different from pre-election poll trends. So a single-digit margin on an exit poll is almost never sufficient to say that a particular candidate will win.
3) Watch out for "The Composite." As they have for the earlier primaries, we expect the web sites of CNN, MSNBC and CBS to post exit poll tabulations shortly after the polls close that will update as the election night wears on (we will post links and commentary here, so we hope you'll plan to check back in later tonight). Those data are weighted to whatever estimate of the outcome the analysts have greatest confidence in at any moment. By the end of the night, the tabulations will be weighted to the official count. Typically, the first waves of exit poll tabulations (including most that leak before the polls close) are weighted to something called the "Composite Estimate," a combination of the exit poll data alone and a "Prior Estimate" that is based largely on pre-election poll results. So if you look to extrapolate from the initial tabulations posted on MSNBC or CNN (as we have done here at Pollster each primary night this year), just keep in mind that in the estimate of each candidate's standing in the initial reports will likely mix exit poll and the pre-election poll estimates (not unlike the kind we report here).
Finally, if you would like more information on how exit polls are conducted, you may want to revisit a Mystery Pollster classic: Exit Polls - What You Should Know. Happy Super Tuesday!
Update: We're live blogging tonight with overall candidate estimates derived from the public exit polls.