Charles Franklin, a University of Wisconsin political science professor and polling authority, said variation between polls occurs, in part, because pollsters interview random samples of people.
"If they all agree, somebody would be doing something terribly wrong," he said of polls. But he also said that surveys generally fall within a few points of each other, adding, "When you get much beyond that, there's something to explain."
The AP-GfK survey included interviews with a nationally representative random sample totaling 1,101 adults, including 800 deemed likely to vote. For the entire sample, the survey showed Obama ahead 47 percent to 37 percent. He was up by five points among all registered voters, including the likely voters.
A significant number of the interviews were conducted by dialing a randomly selected sample of cell phone numbers, and thus this poll had a chance to reach voters who were excluded from some other polls.
It was taken over five days from Thursday through Monday, starting the night after the candidates' final debate and ending the day after former Secretary of State Colin Powell broke with the Republican Party to endorse Obama.
McCain's strong showing is partly attributable to his strong debate performance; Thursday was his best night of the survey. Obama's best night was Sunday, hours after the Powell announcement, and the full impact of that endorsement may not have been captured in any surveys yet. Future polling could show whether either of those was merely a support "bounce" or something more lasting.
During their final debate, a feisty McCain repeatedly forced Obama to defend his record, comments and associations. He also used the story of a voter whom the Democrat had met in Ohio, "Joe the plumber," to argue that Obama's tax plan would be bad for working class voters.
"I think when you spread the wealth around, it's good for everybody," Obama told the man with the last name of Wurzelbacher, who had asked Obama whether his plan to increase taxes on those earning more than $250,000 a year would impede his ability to buy the plumbing company where he works.
On Wednesday, McCain's campaign unveiled a new TV ad that features that Obama quote, and shows different people saying: "I'm Joe the plumber." A man asks: "Obama wants my sweat to pay for his trillion dollars in new spending?"
Since McCain has seized on that line of argument, he has picked up support among white married people and non-college educated whites, the poll shows, while widening his advantage among white men. Black voters still overwhelmingly support Obama.
The Republican also has improved his rating for handling the economy and the financial crisis. Nearly half of likely voters think their taxes will rise under an Obama administration compared with a third who say McCain would raise their taxes.
Since the last AP-GfK survey in late September, McCain also has:
_Posted big gains among likely voters earning under $50,000 a year; he now trails Obama by just 4 percentage points compared with 26 earlier.
_Surged among rural voters; he has an 18-point advantage, up from 4.
_Doubled his advantage among whites who haven't finished college and now leads by 20 points. McCain and Obama are running about even among white college graduates, no change from earlier.
_Made modest gains among whites of both genders, now leading by 22 points among white men and by 7 among white women.
_Improved slightly among whites who are married, now with a 24-point lead.
_Narrowed a gap among unmarried whites, though he still trails by 8 points.
McCain has cut into Obama's advantage on the questions of whom voters trust to handle the economy and the financial crisis. On both, the Democrat now leads by just 6 points, compared with 15 in the previous survey.
Obama still has a larger advantage on other economic measures, with 44 percent saying they think the economy will have improved a year from now if he is elected compared with 34 percent for McCain.
Intensity has increased among McCain's supporters.
A month ago, Obama had more strong supporters than McCain did. Now, the number of excited supporters is about even.
Eight of 10 Democrats are supporting Obama, while nine in 10 Republicans are backing McCain. Independents are about evenly split.
Some 24 percent of likely voters were deemed still persuadable, meaning they were either undecided or said they might switch candidates. Those up-for-grabs voters came about equally from the three categories: undecideds, McCain supporters and Obama backers.
Said John Ormesher, 67, of Dandridge, Tenn.: "I've got respect for them but that's the extent of it. I don't have a whole lot of affinity toward either one of them. They're both part of the same political mess."
(Agencies via China Daily October 23, 2008)
