Pollsters won't admit it, but this years presidential election may be unpredictable.

It is not too close to call merely because polls have John McCain and Barack Obama virtually tied in swing states.

New factors rock the reliability of polling:

TURNOUT: Who will actually vote?

Pollsters interview randomly selected voters, but then weight the results to reflect the expected composition of the electorate in terms of party affiliation, gender, race, age... If the model for turnout is wrong, the poll results could go well outside the margin of error.

Will young voters turn out in record numbers, as they did in many Democratic primaries? Or will Obama-mania fade as he becomes more of a typical politician, changing his positions to be less liberal, and changing his oratory to be less messianic (This is the moment when we must come together to save this planet)?

Both campaigns are courting evangelicals. Obama emphasizes that hes a Christian to counter viral e-mails that he is secretly a Muslim. McCains TV spot spoofing Obama as a Moses wannabe (The One) used language that made some Christian fundamentalists think it was suggesting that Obama is the Antichrist.

When issues are so combustible and complicated, can pollsters plumb the depths of voters souls with simplistic questions?

RACE: pride, prejudice, and guilt

Political analysts wonder if there is a Bradley effect in this years polling, referring to former Los Angeles Mayor Tom Bradley, a black candidate for governor of California who led in polling but lost the election. Apparently many white voters didnt want to admit to pollsters that they opposed a black candidate for fear they would seem bigoted. That could account for Hillary Clinton often outperforming the polls in the primaries against Obama.

Yes, there is white prejudice. But theres also white guilt about racism, which voters might be reluctant to admit as well. Does it offset the prejudice?

There is great pride in, and support for, Obama among African-American voters. Their turnout might increase dramatically. Should pollsters increase the percentage of African-Americans in their polling sample? Or will there be an overall increase in voter turnout, thus offsetting any increase by a subset of the electorate?

AGEISM  and appearance

Americas media culture reveres youth, while old age is often mocked.

McCain would be the oldest first-term president in history, and no one says he looks younger than his age. For voters with high-definition TV, scars and wrinkles are eye-poison.

When McCain and Obama debate, voters will see a greater contrast in appearance than when John Kennedy debated Richard Nixon. Many voters admit to pollsters that theyre troubled by McCains age, but how honest would they be in admitting looks-ism?

TELE-POLLING: privacy and paranoia

Lots of voters have caller ID. When they see a research firms number on the display, many assume its a telemarketer and wont answer. And many voters  not just the young  only use cellphones and dont have a number available to polling firms.

How reliably random is the sample when it consists only of voters who dont mind being asked their opinion by strangers? Surely pollsters fail to capture many voters who are paranoid or protective of their privacy.

Some voters resent the influence of polling in politics and give untruthful answers to be mischievous. (Vegetarian Party Hindu PhD Hispanic I just dont have an accent. Are you calling me a liar?)

UNDECIDEDS: proudly uncommitted

Undecided voters are often uninformed or wishy-washy, rather than independent-minded. Even so, they are exalted in televised focus groups and news interviews. So why wouldnt voters feign indecision?

Reporter: In 2000, you were a soccer mom. In 2004, you were a security mom. Now you are a swing mom. How can a candidate win your support?

Voter: They cant. Ive decided to remain undecided.

Some voters want to seem not only prejudice-free, but opinion-free. Apparently they feel that ignorance is bliss, especially when its shared with a pollster.

PREDICTION: continued unpredictability

This campaign has already been the strangest, most unpredictable of any in memory. Thats been true even after Dennis Kucinich, Mike Gravel, Mitt Romney, and Ron Paul stopped campaigning.

A clear front-runner may emerge after the debates, but for now, polls might not even predict the past.

Todd Domke is a Boston-area Republican political analyst, public relations strategist, and author.

© Copyright 2008 Globe Newspaper Company.