According to the latest poll ... With Election Day approaching, polls are making headlines. But it can be tricky figuring out what they really mean--if they mean anything at all.

• Author: Smith, Patricia
• Position: NATIONAL

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AS soon as the Republican Convention in St. Paul was over last month, pollsters scrambled to measure its impact (as they had for the Democratic Convention in Denver the week before).

Gallup released a poll showing 50 per cent of registered voters favoring Senator John McCain, the Republican candidate, compared with 46 percent for Senator Barack Obama, the Democrat; an ABC News poll found Obama leading McCain 47 percent to 46 percent; and a third poll by CBS News had McCain leading Obama, but by a closer margin of 46 percent to 44.

So what's going on here? Why are there so many different results in the same time frame? The short answer: Polls are complicated.

With the November election just weeks away, the news is filled with polls handicapping the presidential race. Not only are people fascinated by everyone else's opinions; politicians use polls to help tailor their messages to voters, and journalists use them to find out what people care about and why.

Michael Traugott, who studies election polls at the University of Michigan, says political polls have both direct and indirect effects on voters--especially in a tight contest like this year's race for the White House.

"They can stimulate people to give money or to volunteer for a campaign," Traugott says. "They can make people think that their vote is worth more if the margin is close, meaning they have an impact on turnout."

NOT A CRYSTAL BALL

It's just as important, however, to know the limits of what polls can tell us.

A poll tells us about the present, not the future: It's not a crystal ball, but a snapshot d how the public is thinking at a particular moment---and not a perfectly sharp snapshot at that.

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Although a large portion of the American public is committed to one party or the other and holds firm positions on a wide range of issues, there is always a segment that wavers, or stays unconvinced (or uninterested) until late in a campaign. Those "swing voters" ultimately push elections back and forth, and their views can keep changing up to the very last minute.

One of the most embarrassing errors in polling history came in 1948, when the major polling organizations all declared that Thomas E. Dewey, the Republican Governor of New York, would defeat the Democrat, President Harry S. Truman. All of them had stopped interviewing the public several weeks before the election and missed a late swing toward Truman. In addition, a study after the election found their samples had too many middle-income and wealthy people, who were more likely to vote Republican.

Even on election night, political experts were convinced Dewey was going to win--and the photograph of a jubilant Truman holding up a copy of the Chicago Daily Tribune that wrongly declares "Dewey Defeats Truman" has become a political and polling icon.

Today, surveys are conducted right up to Election...