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Bias in Network Polling?

9:27 AM, Oct 31, 2008 • By GARY ANDRES
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While the U.S. economy's declining, national polling is a growth industry. Karl Rove noted on last week's Fox News Sunday that the number of national polls released in October 2008 compared to the same month in 2004 grew by 300 percent (55 national polls were release October 1-23, 2004, compared to 177 during the same period this year).

Examinations into the accuracy of these surveys have already started. This paper paper by professors Leonard Adelman and Mark Schilling argues that broadcast and cable network polling (ABC, CBS, NBC, CNN and Fox) all tilt more pro-Obama in their results than Gallup and Rasmussen. Adelman and Shilling write this:

We compared polls produced by major television networks with those produced by Gallup and Rasmussen. We found that, taken as a whole, polls produced by the networks were significantly to the left of those produced by Gallup and Rasmussen.

We used the available data to provide a tentative ordering of the major television networks' polls from right to left. Our order (right to left) was: FOX, CNN, NBC (which partners with the Wall Street Journal), ABC (which partners with the Washington Post), CBS (which partners with the New York Times). These results appear to comport well with the commonly held informal perceptions of the political leanings of these agencies.

It's important to note the authors make no claims about which polls are more accurate. They simply observe--based on surveys from different outlets that come out the same day--the networks consistently show a more pro-Obama bias (with FOX showing the least Obama tilt and CBS showing the most) compared to Gallup and Rasmussen.

No one from the networks has responded yet. I assume they will wait until after the election. If the networks were right, they'll claim vindication. If wrong? You probably won't hear much about it.

HT: Andrew Gelman