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Reading Between The Lines In The Gardner-Udall Poll

DENVER (CBS4) - Rep. Cory Gardner, trying to unseat Sen. Mark Udall, boasts an eight-percentage point lead over his rival in a Quinnipiac poll released Thursday.

The race is considered one of the most competitive Senate races in the country. The Quinnipiac poll might be an outlier. A USA Today/Suffolk poll has Gardner up by one point. Three other polls conducted in September show Udall leading by as many as six points.

An aggregation of polls by RealClearPolitics.com has Udall leading by a scant 0.6 percent.

Quinnipiac surveyed 1,211 likely voters from Sept. 10-15. The poll has a margin of error of 2.8 percentage points.

DOMINIC DEZZUTTI'S BLOG: Polling: What To Believe & What To Ignore

"Given all the other polls that have been done, can I say it's an outlier? Absolutely," says Norm Provizer, a Metro State University of Denver political science professor. "But to be fair to all parties, I don't know until later on whether the poll, that has results that have come in, is completely off the wall, one of the one in 20 that didn't make it, or whether it's caught the beginning of a trend."

Poll watchers should consider a few factors when determining a poll's accuracy:

* Who conducted the poll: the organization's bias and track record

* Margin of error: that could be enough to sway the results

* How the poll is conducted: what questions are asked, size and makeup of those polled

Many pollsters have a bias, others a skewed sample. Provizer says there's about a 95 percent confidence level with any poll.

"What that means in very simple terms is one out of every 20 polls go completely off the rails," he says.

There are a lot of variables with this year's election because this is the first midterm election that is all mail-in ballots with same-day voter registration.

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