That's too bad. The article is nuanced enough and points out that there are no accepted definitions of either mass shootings or gun free zones and that like many statistics, it depends on how you count. It concludes like this,
"No matter how we spin these numbers, one thing is clear – they can be spun. And they have been. Without a commonly accepted and uniform definition of “mass shooting” or agreement on what constitutes a “gun-free zone,” it’s difficult to settle this debate. Advocates on both sides can point to holes and debatable logic in the reasoning of the study from the other sides."
It seems to me that if one were to have an honest debate it is worthwhile to look at such questions. Sure, I'm liberal and mostly anti-guns, but I didn't post the link just to say, "ha, I'm right and you are wrong", just to add some worthwhile points to the debate.