Explaining the Polls: Is Obama Leading McCain or Is the Race Tied?

Recent polls show a very different race. Here is what the pollsters say.

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A frisson ran through political circles this week when a new Associated Press poll showed the presidential race a dead heat nationally.

The AP poll of likely voters, conducted by GfK Roper Public Affairs & Media, put Democrat Barack Obama at 44 percent and Republican John McCain at 43 percent, a fairly dramatic counterpoint to other national surveys that, on average, have given Obama a consistent lead of just over 7 percent.

What gives? Does the poll truly provide hope to McCain's struggling effort? And in this state-by-state battle for electoral votes, should anyone pay much attention to national numbers, anyway?

To the second question, GOP pollster Whit Ayers answers with a firm "Yes." Changes in the national numbers, he says, predict similar movement in hard-fought states. "Because the battleground states have been moving in concert with the national polling, we should pay attention," Ayers says. "When Obama gains nationally, he tends to gain in the battleground states. When McCain closes nationally, he closes in the battleground states."

But both Ayers and pollster J. Ann Selzer say that the AP poll may be reflective more of how GfK Roper defined the likely voters in their survey than of any significant change on the ground nationally. Compared with a smorgasbord of recent polls, "the AP poll is kind of sitting there alone," says Selzer.

That suggests that Roper used what pollsters refer to as a "restrictive" definition of likely voters. In analyzing polling data, pollsters rely on many models, including those that assess the likelihood that the person polled would show up to vote this year. A "restrictive" analysis, Selzer says, would give much more "likely voter" weight to a person who had voted in past elections, and particularly in recent ones.

Says Ayers: "You end up producing a very different electorate depending on how you determine who is a likely voter. And I suspect that's the explanation" for the AP's results.

However, in this election, if greater weight is given to previous voters and less weight to people who say they will be first-time voters in November—such voters are traditionally believed to be less reliable—the polls risk screening out a large and highly motivated crop of new voters. A recent ABC News/Washington Post poll found that about 10 percent of the electorate this year could be composed of first-time voters. And among those new voters, Obama leads McCain 73 to 26 percent.

Ayers advises that, from the perspective of a consumer trying to make sense of the AP poll and others, "the best way to deal with this sort of variation" is to toss out the poll with the highest margin and the one with the lowest, as well as polls with very small samples, and then average the rest. "If you do that, you can pretty much see where the race is, and if you do that you will find Obama with a single-digit lead somewhere around 7 points," says Ayers, who pays most attention to the daily Gallup Tracking Poll, which relies on daily telephone interviews with at least 1,000 American adults and currently has Obama leading by 7 points.

As Ayers sees it, the polls will continue to track toward Obama. "We tend to want to attribute all movement in these polls to human decisions, to campaign strategy, and campaign tactics—whether brilliant or horrible," he says. But, bottom line, the broader political environment has favored Democrats for months, he says, and voters truly want change. "Ninety percent of the country is feeling disaffected, and McCain was actually in the hunt until the financial meltdown," Ayers says. "But that just reinforced the sense that we have got to have real change. And Obama represents more change."