Pollster: Unlikely to see leaked exit poll results. BOO!!!

[Laura PourMeADrink]

http://www.pollster.com/blogs/looking_for_new_hampshire_exit.php

January 08, 2008
Looking for New Hampshire Exit Polls?

Looking for leaked exit poll results from New Hampshire? Sorry to disappoint, but whatever their merits, we are unlikely to see any such leaked results until moments before the polls close.

In past years, the network consortium that conducts the exit polls distributed mid-day estimates and tabulations to hundreds of journalists that would inevitably leak. In 2006, however, the networks adopted a new policy that restricted 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 just before the polls closed (information that did ultimately leak to blogs). As far as I know, that process will remain in place today.

Here are a few tips for making sense of the exit poll data that you do see tonight:

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 Prior." At least two networks are likely to post exit poll tabulations shortly after the polls close that will update as the election night wears on (try these links for MSNBC and CNN). 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 exit poll tabulations 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 did here on Election Night 2006), 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 New Hampshire Primary Day!


*Clarification: The original version of this post implied that the 1996 overstatement occurred in New Hampshire.

-- Mark Blumenthal