Why the polls have an Obama bias

Brandon J. Gaylord Editor-in-Chief, HorseRacePolitics.com
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The overwhelming majority of public opinion polls show President Obama cruising to re-election. State polls of Ohio, Florida, Virginia, Wisconsin and Iowa are now consistently showing Obama with leads of five points or more.

But Romney is not behind in the polls because liberal Republicans are being turned off or independents are moving toward Obama. Most polls show Romney doing very well within his own party and holding his own with independents. Romney is dropping in the polls because pollsters are predicting a Democratic edge in turnout that will make 2008 look like a good year for the GOP.

For example, the most recent NYT/CBS/Quinnipiac poll of Virginia shows Romney carrying Republicans 95-3 and independents 54-43. In fact, if the poll were weighted the same way that the August NYT/CBS/Quinnipiac poll of Virginia was weighted, Romney would be leading Obama. But because of the increased Democratic lean of the sample, he instead trails Obama by four points.

But the oversampling of Democrats is only a small part of a larger problem. In addition, pollsters are undersampling groups that are sympathetic to Republicans, like evangelicals and people who make over $100,000 a year, and oversampling groups that are sympathetic to Democrats, like mainline Protestants and people who make less than $50,000 a year.

Here’s what Marist is predicting the 2012 electorate will look like in various swing states, relative to 2008:

Republicans                                       Democrats

Iowa  -6.1%                                        Iowa  +5.9%
Colorado  +3.2%                              Colorado  +13.3%
Virginia  -21.2%                               Virginia  -20.5%
Florida  +11.7%                                Florida  +10.8%
Ohio  -9.7%                                         Ohio  -2.6%

Income >100k                                    Income <50k

Iowa  -19%                                          Iowa  +11.6 %
Colorado  -25%                                 Colorado  +68%
Virginia  -14.3%                                Virginia  +20%
Florida  -29.2%                                 Florida  +30.8
Ohio  -14.3%                                       Ohio  +11.4%


Iowa  -22.5%
Colorado  -19%
Virginia  -25%
Florida  +4%
Ohio  -30%

I don’t mean to single out Marist. It’s representative of most of the media polls showing the president on track for re-election.

So why are these polls skewing so far left? Conservative conspiracy theories tying the polls to mainstream media bias fail to acknowledge the need for pollsters to retain professional credibility. They can’t do that if they are consistently making bad predictions. I think the problem is that pollsters are so focused with ensuring that Democratic-leaning groups — especially minorities — are fairly represented in their polls that they’re failing to ensure that Republican-leaning groups are also fairly represented in their polls.

Of course, it’s possible that the pollsters are right. Perhaps minority voters will turn out in even higher numbers in 2012 than they did in 2008. Maybe Republicans who are not sold on Mitt Romney will stay home. If that’s the case, President Obama really will cruise to re-election.

Brandon J. Gaylord, the editor-in-chief of HorseRacePolitics.com, is a graduate of George Washington University’s Graduate School of Political Management. Brandon got his start in politics as an intern in Vice President Richard Cheney’s Office of Political Affairs.