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Our Polls Are on the Mark. I Think.

There is also the possibility of a pre-election "bandwagon effect." Post-election surveys frequently overstate support for the winner, and with 70 percent of respondents in a recent Gallup poll saying that Obama is headed for victory on Tuesday, perhaps voters are beginning to overstate the likelihood that they'll vote for him. (There's no precedent for something like this happening, but hey, it's been a weird year.)

I worry more about a basic concern: whether we are getting a truly random sample of opinion. Pollsters bank on the fundamental notion that the people who answer our calls are similar to those who don't, and we have reams of data justifying those assumptions. But what if the people who pause to take a pollster's question are significantly different from those who don't?

After all, fewer and fewer people have been taking our calls over the years. The Pew Research Center, which has done extensive research into declining survey-response rates, has found that poorer, less educated whites -- who tend to hold somewhat less positive views toward African Americans -- are also harder to get on the phone than those who have higher incomes and more formal education. My fellow pollsters and I give this a pretty academic name, "differential nonresponse," but it's a live, practical concern.

Despite my list of worries, a few things remain clear to me: Not all polls are created equal. We've been bombarded with polls that fell far short of the methodological rigor required for a good survey. If you mix in bad polls with the good ones, as happens all over the Web, you just may get dodgy results.

I also remind myself that humility is built into my field's DNA. The mathematics of the "random sample" on which all polling is based says that five times out of 100, we will be badly off the mark. Call it the pollster's law of averages.

But these seem to be topics for another day. The polls appear to be in general agreement that Obama is ahead; the only question is by how much. And this time, the pollsters' findings are being reinforced by the work of two other groups of campaign obsessives: the political scientists who use predictive models drawn from past election results to predict the next one (the one professor whose forecast had McCain headed for victory has "adjusted" his model), and the reporters out there knocking on doors and interviewing voters.

That reassures me because it suggests that 2008 is not like 1980, a year in which some late polls showed a close race between Jimmy Carter and Ronald Reagan. But shoe-leather reporting -- such as the 50-state roundup, led by David S. Broder, that The Post published the Sunday before the election -- found that Reagan was surging. Today, all the indicators -- not just the polls -- suggest that Obama is the candidate with momentum. If that changes over the final days, quality polls will still be the single best gauge of why things shifted.

Of course, if the trustworthy polls continue showing Obama ahead and McCain wins, it would be a monumental failure for political scientists, reporters and pollsters alike -- an indictment worse than New Hampshire, worse even than 1948. I think the quality pollsters have done a good, professional job this year. I don't think we'll get bitten. Even so, I'll be a little worried until it's all over. I'm not sure what kind of night I'll have on Tuesday. But I'm sure I'm going to have a nervous one on Monday.

Jon Cohen is The Washington Post's polling director.

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