Wednesday, June 15, 2005

Maybe we're just better looking than they are


Before reviewing the problem with the exit polls, let's look at how wrong they were. According to a report released by pollsters on Jan. 19 (click here for a PDF copy), the exit polls tended to predict Kerry doing better than he ultimately did, both nationally and in many states. In 26 states, the exit poll overstated Kerry's share of the vote by a significant amount, more than what statisticians call "one standard error." There were only four states in which the exit polls overstated Bush's share of the vote by more than one standard error.

Mitofsky [ a pollster, ] says it's impossible to say precisely why more Kerry voters than Bush voters participated in exit polls. Were Kerry voters simply more willing to speak to pollsters? Were pollsters more willing to speak to Kerry voters? Or, conversely, were Bush voters less willing to talk? Were pollsters less willing to seek out Bush voters? It's likely that some mix of such "motivational factors" contributed to the biased exit poll, Mitofsky says, but at this point it's not possible to determine why some voters were willing to be interviewed, why some were not, and what the interviewers were thinking at the time.

But Mitofsky has some clues. Exit polls are conducted by an army of interviewers -- usually people just looking for a good short-term job, including many college students; 35 percent of the interviewers were between the ages of 18 and 24, and most were women -- who fan out to more than 1,000 pre-selected precincts across the country. Because any poll depends on its respondents being selected randomly, the pollsters are each assigned a number, from 1 to 10, that represents the "rate" at which they're supposed to attempt to approach a voter. An interviewer given a rate of 1 should attempt to interview every single voter that leaves a voting precinct; an interviewer with a rate of 10, reserved for large precincts with many voters, must only approach every 10th voter for an interview.

What Mitofsky finds most striking about the polling data is that the precincts with the largest "error" tended to be those with the largest interviewing rate.

That would explain it; I mean, did you ever see what those Bush voters looked like?

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