BOULDER, CO - OCTOBER 28: Presidential candidates Donald Trump (L) speaks while Ben Carson looks on during the CNBC Republican Presidential Debate at University of Colorados Coors Events Center October 28, 2015 in Boulder, Colorado. Fourteen Republican presidential candidates are participating in the third set of Republican presidential debates. (Photo by Justin Sullivan/Getty Images)

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.