Why Presidential Polls Vary So Much

Robert Roy Britt

Date: 31 October 2008 Time: 06:33 AM ET

A Fox News poll has John McCain down just 3 points in the polls, stating: "The race has tightened with Barack Obama now leading John McCain by 47 percent to 44 percent among likely voters."

A CBS News/New York Times poll has Barack Obama up by 11 percentage points, 52 to 41, among likely voters nationwide. Earlier this week there were polls suggesting the race was too close to call. Some variations result from whether likely voters are polled vs. any, um, Joe. The way questions are phrased has a big effect, too. In the end, polls are typically flawed, one expert says. Among the problems: People without land lines are often excluded, and people change their minds.

McCain's team is banking on the polls being wrong. From the WashPost: "The country, they say, could be headed to a 2008 version of the famous 1948 upset election, with McCain in the role of Harry S. Truman and Sen. Barack Obama as Thomas E. Dewey, lulled into overconfidence by inaccurate polls."

As an election nears, however, polls tend to become more accurate. The Gallup organization has a long list of polls vs. results in previous presidential elections that show them doing pretty well in their final surveys prior to election. In 1984, they accurately predicted Ronald Reagan's landslide (59 percent) over Walter Mondale. However, in 2004 Gallup had George W. Bush and John Kerry deadlocked at 49 percent, yet Bush won 51/48. The deviation was tiny (just 2 percent) but, of course, huge.

CNN's Poll of Polls might have some merit, especially so close to Nov. 4 ... it simply aggregates all these flawed surveys into one, finding now that "50 percent of likely voters are backing Sen. Obama for president, with 43 percent supporting Sen. McCain and 7 percent undecided" (and revealing that there are a lot of undecided voters. (Also check out RealClearPolitics exhaustive poll averaging page.)

Finally, however, a new study finds that most undecided voters probably have made their minds up, they just don't know it.

"Undecided voters may have decided implicitly before they know that they have explicitly," said researcher Brian Nosek, a psychology professor at the University of Virginia. Of course, Nosek's conclusion is based on ... a survey. [People have been shown to flat our lie in sex surveys. Might political surveys suffer same?]

However, Patrick Campbell, a 50-year-old Air Force Reserve technician, expressed genuine indecision: "I'm split right down the middle," Campbell told AP. "Each one has things that are good for me and things that are bad for me. And people like me."

Keep in mind: Presidential elections are won by winning states. Politico reports that the candidates are evenly matched in two key swing states, North Carolina and Missouri.

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