The economists Stefano DellaVigna (UC Berkeley) and Ethan Kaplan (Stockholm University) have published the final version of their paper “The Fox News Effect: Media Bias and Voting” in the Quarterly Journal of Economics (sub. req. – see also an earlier non-gated version). Here is the abstract, which summarizes a striking result that has apparently held up under scrutiny:

Does media bias affect voting? We analyze the entry of Fox News in cable
markets and its impact on voting. Between October 1996 and November 2000, the
conservative Fox News Channel was introduced in the cable programming of 20
percent of U. S. towns. Fox News availability in 2000 appears to be largely
idiosyncratic, conditional on a set of controls. Using a data set of voting data for
9,256 towns, we investigate if Republicans gained vote share in towns where Fox
News entered the cable market by the year 2000. We find a significant effect of the
introduction of Fox News on the vote share in Presidential elections between 1996
and 2000. Republicans gained 0.4 to 0.7 percentage points in the towns that
broadcast Fox News. Fox News also affected voter turnout and the Republican
vote share in the Senate. Our estimates imply that Fox News convinced 3 to 28
percent of its viewers to vote Republican, depending on the audience measure. The
Fox News effect could be a temporary learning effect for rational voters, or a
permanent effect for nonrational voters subject to persuasion.

DellaVigna and Kaplan have also posted a forthcoming edited volume chapter titled “The Political Impact of Media Bias” that explores their results in more detail. Here is part of the introduction:

We use our estimates of the
impact of Fox News to compute persuasion rates, that is, the share of Democratic
voters that switched to voting Republican because of exposure to Fox News. We
also compute mobilization rates, that is, the share of non-voters that turn out to
the polls because of exposure to Fox News. This section expands substantially
on the discussion of persuasion rates in DellaVigna and Kaplan (2007). In our
baseline calibration, we estimate that 4 to 8 percent of the audience was persuaded
to vote Republican because of exposure to Fox News. When we allow for a separate
effect on non-voters, we find that the mobilization effect of Fox News may have
accounted for one sixth to one hundred percent of the impact. We obtain similar
persuasion rates for the effect of Fox News on US Senate elections. These estimates
imply a sizeable, and large in some specifications, impact of the media on political
decisions.

Note to the haters: If this result seems obvious, remember (as I’ve pointed out before) that it is difficult to show cause and effect when studying the media because the outlets’ audiences are self-selected. Thus, showing that Fox viewers are mostly conservative would tell us nothing about whether watching the channel made them more conservative. In this case, DellaVigna and Kaplan are exploiting the idiosyncratic rollout of the channel across the country to estimate an exogenous effect on aggregate turnout and voting.