Disparity among presidential polls

Polls agree that McCain is the underdog. After that, you have got reports that are all over the board about where the race is going.

This week an AP poll called the race a dead heat.

CNN reporter: "With just two weeks left in the presidential race, one poll suggests John McCain has all but erased Barack Obama's lead in the race for the White House,"

While MSNBC looked at another and suggested a landslide for Obama.

MSNBC reporter: "These numbers are getting up in the double digit level."

That is a big difference this late in the campaign, says ABC7's political analyst Professor Bruce Cain.

"And the reason, for the most part, is the assumptions that they're making about turnout," said Cain.

Some polls assume the turnout of Republicans and Democrats will be relatively even. Other polls look at the Democratic advantage in voter registration and give Democrats as much as a nine or ten-point advantage.

Critics of the AP poll say it failed to take into account a large number of college age voters who are registering Democratic.

"And once you factor in those turnout differences, you're going to get very different polling results," said Cain.

And there is also a difference in the quality of the polling. For example, this week the Investor's Business Daily, or IBD poll, reported McCain within one point of Obama, until you look at the poll's particulars.

"According to the IBD poll, voters between the ages of 18 and 24 are three-to-one for John McCain. Three-to-one for John McCain, voters between the ages of 18 and 24, well that's simply not credible," said Cain.

Credible or not, RealClearPolitics.com takes the national polls and averages them together. Karl Rove used that number this week to assert that McCain is gaining.

"Take a look at Real Clear Politics, for example, the average of all the polls, a week ago it was ten points, today it's five points," said Rove.

Rove exaggerated. In the poll he is talking about, Obama's lead did dip a bit earlier this week, but since then his lead has widened.

"I looked at 11 different national polls last night. Barack Obama is ahead in every one of them. In five of them he's got a double digit margin, in seven he's at 50 percent or higher," said Democratic strategist Paul Maslin.

Maslin says what is significant are the polls in the battleground states like Ohio or Florida where Obama has a slight edge, or in states like Virginia that have been Republican, but are now leaning towards the Democrat.

Rove's own electoral vote projection shows that for now Obama has 306 to 171 advantage.

"The question is just how different will it be. How much of an edge will the Democrats have in the turnout and that's the unanswerable question right now," said Cain.

We also hear a lot about voters telling pollsters they will vote for an African American when in fact they won't -- the so-called Bradley effect. Professor Cain, like most analysts, is discounting that effect in the current campaign because in the primaries Obama's projected numbers turned out to be pretty close to the actual count. However, remember in that case those voters polled were likely all Democrats.

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