How much bias would there have to be for all of the polls to be wrong?

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On the above graph of the poll of polls, President Obama is now only 0.4 percentage points down from his implosion on October 3. Nate Cohn believes Obama’s odds are good:

The polls are quite consistent and clear in the battleground states worth 270 electoral votes. With Obama above 49 percent in Nevada, Wisconsin, and Ohio, a wave of undecided voters can’t flip the outcome. At this point, the polls must be wrong for Romney to prevail. The polls have been wrong before and they will be wrong again. The race is close enough for the polls to conceivably get one of those states wrong, but the odds are against it.

Kevin Drum accounts for polling error:

[S]uppose there is a systematic bias in the polls. How big would it have to be in order for Romney to win? This is what Sam Wang’s “meta-margin” tells us, and it currently stands at 2.72%. That’s how far off the polls would have to be—either because undecideds break heavily for Romney or because the pollsters’ likely voter screens are wrong—in order for Romney to win, and it’s a pretty big number. It’s unlikely that either of these effects is anywhere near that large.

Peter Schorsch is the President of Extensive Enterprises and is the publisher of some of Florida’s most influential new media websites, including SaintPetersBlog.com, FloridaPolitics.com, ContextFlorida.com, and Sunburn, the morning read of what’s hot in Florida politics. SaintPetersBlog has for three years running been ranked by the Washington Post as the best state-based blog in Florida. In addition to his publishing efforts, Peter is a political consultant to several of the state’s largest governmental affairs and public relations firms. Peter lives in St. Petersburg with his wife, Michelle, and their daughter, Ella.