Study: Guns Don't Kill People, 'Stand Your Ground' Laws Do

A new study released by Texas A&M University argues that not only do "Stand Your Ground" laws – like the Lone Star State's Castle Doctrine – not deter crime, they actually increase murder rates, perhaps making the argument for anti-gun advocates who wish to see the laws struck down.

The report comes during a time where self-defense laws are facing more scrutiny following the February shooting death of 17-year-old Trayvon Martin. The man who shot Martin, 26-year-old George Zimmerman, says he acted in self-defense in accordance with Florida's suddenly controversial "Stand Your Ground" legislation.

The study goes on to argue that it is "clear" these types of laws result in increased death.

"Regardless of how one interprets increases from various classifications, it is clear that the primary effect of strengthening self-defense law is to increase homicide," the report reads, written by Cheng Cheng and Mark Hoekstra of the Texas A&M Department of Economics.

At least 23 states have adopted their own versions of Castle Doctrine or Stand Your Ground laws, which remove the "duty to retreat" and gives citizens the right to use deadly force against an attacker if there is no other option.

More from the study:

"We find the laws increase murder and manslaughter by a statistically significant 7 to 9 percent, which translates into an additional 500 to 700 homicides per year nationally in states which have adopted Castle Doctrine."

"One theory is that these are in some sense legitimate self-defense killings that just don't meet the strict definition of justifiable homicide."

"While castle doctrine law may well have benefits to those protecting themselves in self-defense (meaning the individual cases where a person uses a weapon to deter a specific crime), there is no evidence that the law provides positive spillovers by deterring crime more generally."

"We now turn to whether strengthening self-defense laws causes an escalation of violence. Given that the laws reduce the costs associated with using violence, economic theory would predict that we would get more of it. Perhaps the most obvious form of escalation—and one most commonly cited by critics of castle doctrine law—is that conflicts or crimes that might not have otherwise turned deadly may now do so. For example, a criminal may not have intended to kill someone he was robbing until the victim attempted to use a weapon in self-defense. "

Cheng and Hoekstra also argue that strengthening concealed carry gun rights and Castle Doctrine laws has no "meaningful deterrence" on theft-related crimes. They said this surprised them.

"We would expect that these crimes would decline after the adoption of castle doctrine, to the extend that criminals respond to higher actual or perceived risks that the victims will use lethal force to protect themselves," they added.

Their explanation? Instead of thinking twice about invading a home that is protected by a Castle Doctrine, illogical criminals instead may choose to arm themselves as well, turning a routine burglary into a potential shooting death. They say criminals – and some of the "general public" – aren't able to determine the likelihood of someone using deadly force against them.

"This is true not just of criminals, but of the general public: when it come to things that involve probabilistic thinking, people have a pretty hard time with it...'What's the increase in the possibility that someone will defend themselves with lethal force against me?' It's tough to answer that in a super rigorous way, Hoekstra told the Dallas Observer. "The idea that a criminal is going to do a really great job of answering that, and if they'd be able to make these calculations -- You're asking a lot of anybody to make that calculation."

Just to clarify for our audience, the possibility of bodily harm is probably more likely when you are committing a crime or invading someone's home or property.

But the researchers also agree there is probably more than just self-defense law behind their findings:

"We suspect that self-defense situations are unlikely to explain all of the increase, as we also find that murder alone is increased by a statistically significant 6 to 11 percent."

The Dallas Observer provides some additional insight:

Hoekstra and his co-author, grad student Chen Cheng, looked at 23 states where castle doctrine laws exist and found slight evidence that castle doctrine increases justifiable homicides committed by civilians by anywhere from 17 to 50 percent. That sounds like a lot. But the reality is that justifiable homicide is narrowly defined and exceedingly rare: according to the FBI, a killing can only be classified that way when someone kills another person who's committing a felony. Fewer than 200 deaths are classified that way each year.

The homicide increase also presents another issue for the researchers. How do you determine who died in a castle doctrine situation: the alleged criminal or the person allegedly defending themselves? The FBI data Hoekstra and Cheng studied doesn't show that kind of detail, and Hoekstra says it's crucial in figuring out what's driving the homicide increase. The answer, he says, is another study.

"The best idea I've come up with is to try to figure out if the people getting killed have criminal backgrounds," he says. "If you see an increase in people getting killed without criminal backgrounds then at least part of what it suggests is escalation." But, he concedes, "It's going to be difficult. I don't know how optimistic I am."

It may be worth while to point out, even in the aftermath of the Trayvon Martin case, roughly 56 percent of Florida residents still support Stand Your Ground in the Sunshine State, according to a Quinnipiac University study.

You can read all Texas A&M University's study on self-defense laws here.