"Free speech" seems pretty nebulous and ill-defined here. It'd be nice to see some objective measures be analyzed rather than the only data be student surveys (maybe a measurement of speaker viewpoint diversity over time?). and these survey are about what speakers should be allowed to make speeches hosted by the school... seems like a very specific aspect of campus speech.
For a different measure of how much free expression is allowed- maybe look at often people are killed for expressing controversial views. I'd invite anyone to contrast Nate's article with the story of the Kent State students in the 1970s who were summarily executed by the US army for peaceful protests[1], is FIRE and Nate Silver really going to argue modern campuses "free speech" is in trouble now more than back then? Public protest seems like it should be much more protected (and relevant to the term 'free speech') than who-gets-what speaking fees.
For a different measure of how much free expression is allowed- maybe look at often people are killed for expressing controversial views. I'd invite anyone to contrast Nate's article with the story of the Kent State students in the 1970s who were summarily executed by the US army for peaceful protests[1], is FIRE and Nate Silver really going to argue modern campuses "free speech" is in trouble now more than back then? Public protest seems like it should be much more protected (and relevant to the term 'free speech') than who-gets-what speaking fees.
[1] https://en.wikipedia.org/wiki/Kent_State_shootings