Measuring political bias in media

December 30th, 2006

media biasWhich headline would make you buy a newspaper?

  • Winning the global war on terror by repealing the death tax and solving the medical liability crisis
  • Winning war in Iraq by bringing our troops home and raising fuel economy standards

I ran across an article on Slate, How To Speak Republican … or Democratic. that talks about an academic paper and it’s methodology to measure political slant in newspapers.

Gentzkow, Matthew Aaron and Shapiro, Jesse M., What Drives Media Slant? Evidence from U.S. Daily Newspapers, November 13, 2006.

The working paper by University of Chicago economists Gentzkow and Shapiro is really interested in explaining why newspapers are biased. Their answer, not surprisingly, is profit. (They are economists, after all). Their methodology and results are of interest to those of us who would like to develop better techniques for detecting and measuring source bias.

From the paper:

“In this paper, we propose a new index of ideological slant in news coverage, and compute it for a large sample of U.S. daily newspapers. … Our slant index measures the frequency with which newspapers use language that would tend to sway readers to the right or to the left on political issues. To do this, we examine the set of all phrases used by members of Congress in the 2005 Congressional Record, and identify those that are used much more frequently by one party than by another. We then index newspapers by the extent to which the use of politically charged phrases in their news coverage resembles the use of the same phrases in the speech of a congressional Democrat or Republican. Underlying this approach is a revealed preference assumption; namely, that the language chosen by speakers with a political agenda will tend to persuade listeners to support that agenda.”

The paper’s appendix has a list of the two and three word phrases they used to measure bias.

To test their slant identification methodology, they compared their results to those from Mondo Times, an online media guide. I thought that these human judgments of political bias provide an interesting resource as well.