At tonight's GOP debate in Boulder, Co., Donald Trump made the oft-repeated claim that mass shooters specifically target gun-free zones for their rampages.

"I feel that the gun-free zones and, you know, when you say that, that's target practice for the sickos and for the mentally ill," he told moderator Carl Quintanilla. "That's target [practice]. They look around for gun-free zones."

But little data supports this claim. For starters, if you probe the reasons why shooters target particular places, you typically find that gunmen have a grievance attached to a particular location. A Mother Jones analysis of mass shootings between 1982 and 2015 found not one single instance where the gunman appeared to be motivated by the knowledge that a place was gun-free.

Rather, gunmen usually had specific grievances that they chose to take out at certain locations: a workplace, or a federal facility, or a school, for instance. The FBI's 2014 study of 160 active shooter incidents found that in many cases, shooters had a specific connection either to the place where the shooting occurred, or with somebody who worked there.

And a 2014  analysis by a gun control group of 110 mass shooting incidents between January 2009 and July 2014 found that only 14 percent of those shootings took place in a so-called "gun-free" zone.

As Evan DeFilippis and Devin Hughes point out at The Trace, the claim that shooters target gun-free zones runs contrary to another claim frequently made by gun rights advocates: that mass shootings are primarily a function of mental health and not of gun laws. But the claim that mass shooters rationally seek out gun-free areas in order to encounter the least resistance runs a tension with the notion that shooters are mentally ill individuals with an irrational axe to grind.