Salena Zito

Two weeks ago, Newsweek released a poll showing Barack Obama 15 points ahead of John McCain. Days later, the Los Angeles Times/Bloomberg poll showed a similar gap.

Yet over at Gallup, the daily tracking poll showed the two presumptive presidential nominees remain in a statistical tie, although early last week Obama did start to break a nickel ahead of McCain.

The question that arises for the average person watching this race is, why the zero to 15-point difference in polling data? Is one poll more accurate than the other?

“All polls are not created equally,” says Republican pollster Neil Newhouse. “How a poll is conducted and its attention to detail is extraordinarily important.”

Newhouse explains that accurate sampling is critical and the lack of it explains the wild differences in polling data.

“Senior citizens represent around 21 percent of the electorate, yet some polls include far more than that percent in their polling simply because seniors are easier to reach on the phone,” he says.

“Ignoring details like that can skew results from poll to poll,” says the Democrats’ legendary media consultant Dane Strother.

Another reason why early polls are all over the map “and downright suspicious,” Strother says, is because people don’t know what the “screen” is.

Simply put, a screen is who is or is not allowed to participate in the poll.

Without knowing the screen or the way that questions are phrased, Strother says you really can’t tell if a poll captures a true reflection of attitudes, “which explains why these polls are all over the place.”

Newhouse and Strother agree that the only polls that are truly accurate must have “likely voters” asked the question as part of the equation, not just the ambiguous “adults,” which are the easier of the two to sample.

Newspaper polls typically are described as “snapshots in time” that do not account for the ongoing flow of a campaign. Consequently, they can spike in one direction or another, depending on the news being reported during the survey period.

For example, a survey conducted on the Friday and Saturday of the “Unity” event in New Hampshire would be tainted by Sen. Hillary Clinton’s endorsement of Obama.

In contrast, the Gallup poll is a “tracking survey” that is taken nightly, reflecting the mood over a three- or four-night period -- and resulting in a more even view of the electorate and its impressions of the race.

Then there are “push” polls, which are not really polls at all. Instead, they’re a mechanism designed not to determine voters’ opinions but to disseminate negative information about a candidate in order to move voters away from that candidate.

Salena Zito

Salena Zito is a political analyst, reporter and columnist.