Five myths about political polls

At a minimum, excluding cellphones means these polls are increasingly reliant on statistical weighting. They might make up for a lack of young people, for instance, by counting several times the answers from the few younger respondents. Peter Miller, a recent president of the American Association for Public Opinion Research, points out the root problem with weighting: “The more you rely on weights, the more you risk being wrong for reasons you don’t understand.”

It is always better to look at polls’ methodology, not just their results. What’s more, the “horse race” findings are often among the least important parts of a good poll. What issues motivate voters? And who is motivated to vote? These are more crucial to understanding an election than whether a candidate is up two, three or six percentage points.

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4. Polls are skewed if they don’t interview equal numbers of Democrats and Republicans.

Political junkies quickly scan each poll release to see the “party ID split” — the proportions of self-identified Democrats, Republicans and independents in the sample. It makes sense: With party loyalty as strong as it is, the numbers of Democratic and Republican respondents in a survey make a huge difference. But to think, as many do, that there should be equal numbers from each party is off-base, particularly when looking at polls meant to assess the general population’s views.

Though voters seem split down the middle, there have generally been more Democrats than Republicans in the country since pollsters started tracking partisan allegiances after World War II. There is often more parity in election tallies, as Republicans tend to be more reliable voters than Democrats, but that also depends on the year.

Artificially evening out a poll’s partisan balance or arbitrarily setting it to match someone’s guess at turnout on Election Day may make one side a bit happier — but at the expense of distorting the current state of play.

5. News outlets are biased in presenting polls favorable toward President Obama.

Media-bashing is at a peak among conservatives, and some on the right routinely dismiss any poll showing Obama ahead of Romney. (And some on the left reflexively scorn polls in which Romney leads.) Before recent surveys turned in Romney’s direction, one conservative blogger went so far as to set up UnskewedPolls.com, a site offering “adjusted” public polls, tilted to favor Romney by manipulating the samples to be more Republican.

In truth, news organizations have only one bias — toward news.

Nothing demonstrates this better than the recent coverage of the Pew Research Center’s post-debate national poll, which showed big, across-the-board movements from Obama toward Romney. The Washington Post splashed the poll on its front page, and the survey provided days of fodder for cable news, illustrating that the media gravitate toward a competitive race, big shifts and conflict much more than one political party or the other.

cohenj@washpost.com

Jon Cohen is The Washington Post’s polling director.