Ethan Kaplan writes:

I just happened upon a post of yours on the potential impact of Fox News on the 2016 election [“No, I don’t buy that claim that Fox news is shifting the vote by 6 percentage points“]. I am one of the authors of the first Fox News study from 2007 (DellaVigna and Kaplan). My guess is that the reason the Martin and Yurukoglu estimates are so large is that their instrument is identified off a group of people who watch Fox because it is higher in the channel order. My guess is that such potential voters are decently more likely than the average voter to be influenced by cable news. Moreover, my guess is that there are not a huge number of such people who actually do spend tons of time watching Fox News. Moreover, there may be fewer of such people than in the year 2000 when U.S. politics was less polarized than it is today and when Fox News did not yet have as much of a well-known reputation for being a conservative news outlet.

Interesting example of an interaction; also interesting example of a bias that can arise from a natural experiment.