Moore: "Swing Voters" Redux - CBS/NYT vs. Gallup

07/17/2008 10:27 am ET | Updated May 25, 2011

Today's Guest Pollster article comes from David W. Moore, a senior fellow with the Carsey Institute at the University of New Hampshire. He is a former vice president and senior editor with the Gallup Poll, where he worked for 13 years, and is the founder and former director of the UNH Survey Center. He manages the blogsite, Skeptical

In a post last week, I suggested the size of the group that Gallup calls "swing voters" was probably a significant under-estimate of the actual proportion of the electorate that is up for grabs. A new CBS/New York Times poll seems to confirm my suspicions, reporting the equivalent swing voter group at one and a half times greater than what Gallup reported - 36 percent vs. 23 percent respectively.

The Gallup report defined "swing voters" as those who were "undecided" (6 percent), plus those who initially supported one of the two major candidates but then admitted they could change their minds before election day (17 percent). The same criteria, applied to the CBS/NYT poll, suggest a larger swing voter group because this poll has a larger undecided group than the Gallup poll (12 percent), and a larger number of voters who initially chose a candidate but said it was too early to say their minds were made up (24 percent).*

There is almost a month between the two polls, Gallup's conducted June 15-19 and the CBS/NYT poll conducted July 7-14. So, the difference in the size estimates of the swing voter group could be a function of time. If so, that leads to the somewhat counterintuitive conclusion that this past month's campaigning has led to an increase in voter uncertainty, rather than the reverse, as more conventional frameworks might predict. I'm not a fan of this unconventional theory, though CBS reports that according to their poll, the undecided vote increased from 6 percent to 12 percent in the past month. Still, I suspect the differences between the two polls are mostly caused by house effects, but it would be hard to prove one way or the other.

In my post last week, I suggested the actual proportion of the electorate up for grabs is probably greater than the 40 percent figure, found by Gallup in September 1996 in the Robert Dole - Bill Clinton contest. The CBS/NYT poll lends credence to my suspicions, even though it also used the forced-choice format ("who would you vote for if the election were held today?") that Gallup used last month. In September 1996, Gallup first asked if voters had made up their minds, and then asked voters who they preferred. If the CBS/NYT poll had used that format this time, it almost certainly would have found a larger group of swing voters than the 36 percent they just reported.

In any case, CBS has rightfully emphasized in its headline the most important conclusion from these data: "Obama Leads But Race Looks Fluid." Too few pollsters, and too few news organizations, are looking at the fluidity of the electorate. Instead, like the New York Times article, they let stand the forced-choice horserace numbers as though such figures are solid estimates of voter intentions.

While I applaud CBS and Gallup for pointing to the fluidity of the race, I think it's worthwhile saying again that the uncertainty in the race is not because many voters may change their minds before election day, but rather because many voters have not yet made up their minds. The notion that 90 percent or more of voters have already come to a conclusion as to whom they will support (even a conclusion they can change) is highly misleading - an artifact of poor question wording that pollsters should have long since modified.

* The CBS/NYT poll shows that 28 percent of those who initially made a choice then admitted their minds were not made up. The table shows that 86 percent made a choice (45 percent for Obama, 39 percent for McCain, 2 percent for other). The two percentages multiplied by each other give 24 percent. The latter figure added to the 12 percent who originally said they were undecided produces a 36 percent total for "swing voters."