Study knocks ‘Stand Your Ground’

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Posted: Sunday, June 24, 2012 12:00 am

A new Texas A&M study has found that the Castle Doctrine – on which Florida's controversial "Stand Your Ground" law is based – does not deter crime and, in fact, increases the murder rate.

 “This study provides further evidence that ‘stand-your-ground’ legislation does more harm than good,” NAACP President and CEO Benjamin Todd Jealous said in a statement. “Too often these laws provide cover for vigilantes and hate groups who choose to take the law into their own hands. They have led to an increase in homicides, and people of color seem to always get caught in the crossfire.”

The study finds that these laws increase murder and manslaughter by a statistically significant seven to nine percent. The study also finds that they have no “meaningful deterrence” on theft-related crimes.

The killing of Florida teen Trayvon Martin by neighborhood watch volunteer George Zimmerman in late February launched thousands of arguments about Castle Doctrine laws, which allow a person to use lethal force against an intruder in certain situations, provided they have a reasonable fear of death or serious bodily harm. Lawmakers in several states, including Texas, have debated revising their own self-defense laws.

"We found a seven to nine percent increase in homicides," says one of the study's authors, associate economics professor Mark Hoekstra. "That's significant. That's robust. We did comparisons in a bunch of different ways. We compared states that adopt (the law) to states that don't adopt. It doesn't matter if you control for things like policing or levels of incarceration. You can compare to only other states in the same region. It doesn't matter. At the end of the day, Castle Doctrine increased homicides by seven to nine percent."

Hoekstra and his co-author, grad student Chen Cheng, looked at 23 states where Castle Doctrine laws exist and found evidence that the Castle Doctrine increases justifiable homicides committed by civilians by anywhere from 17 to 50 percent. 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.

Instead, the study found that the Castle Doctrine increases total homicides, including murder and non-negligent homicide, by 500 to 700 additional deaths per year. Hoekstra says they see three distinct possibilities that might account for the increase.

"One theory is that these are in some sense legitimate self-defense killings that just don't meet the strict definition of justifiable homicide," he said. "On the other hand, it could be that the increase in homicide is due to criminals escalating. So one possible response to the Castle Doctrine is for criminals to carry and use guns more frequently, for example. We could be picking up the effect of that. The third possibly is that otherwise non-lethal conflicts turn deadly because of Castle Doctrine. It's really, really difficult to distinguish between those three possibilities."

In 2005, Florida became the first state to legally expand self-defense protections by removing the duty to retreat before using lethal force outside one’s own home, as well as by adding other provisions that address civil liability and a “presumption of reasonable fear” when acting in self-defense. Twenty-two other states have passed similar laws, though some are more restrictive than others.  

The term “Castle Doctrine” comes from the English common law principle that people have no duty to retreat before using lethal force in self-defense when in their own home, or castle. The purpose of the laws is to help victims better protect themselves against violent crime.  

For their study, Hoekstra and Cheng analyzed state-level crime data from 2000 to 2009 from FBI Uniform Crime Reports. They began their initial investigation last summer, well before the Martin case pushed self-defense laws into the spotlight. 

To the untrained eye, their research doesn’t fall into a category of traditional economics, but Hoekstra says it is all about incentives.

“When you change self-defense law, you change incentives. You change the incentives of people protecting themselves — now it’s lower cost to use lethal force, for example, after a state passes a Castle Doctrine law,” Hoekstra said. “So … on the one hand you might expect to get more lethal force because you lowered the cost, and on the other hand, you might expect to get less crime because you raised the expected cost to criminals.”

But as Hoekstra found, the results indicated only that there was an increase in the use of lethal force. The main question now, Hoekstra says, is why homicides increased.

“I think there are several reasonable explanations for why homicides would go up, but I’m not sure which one is true,” he said. “It could be that the increase in homicides is driven by an increase in self-defense killings. On the other hand, it could be that the increase in homicides is due to an escalation of violence in otherwise nonviolent situations.”

The study says that self-defense alone probably doesn't explain the numbers, though.

"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," they write." "This is important because murder excludes non-negligent manslaughter classifications that one might think are used more frequently in self-defense cases. But 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."

Any hope that criminals in Castle Doctrine states might be deterred from robbing you by the knowledge that you could be packing heat are also incorrect.

"This is true not just of criminals, but of the general public: when it comes to things that involve probabilistic thinking, people have a pretty hard time with it,” he said. “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. 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."

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," Hoekstra said. "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."


Texas A&M University and the Dallas Observer contributed to this report.

Zack Burgess is the Enterprise Writer for The Tribune. He is a freelance writer and Editor who covers culture, politics and sports. He can be contacted at and followed on Twitter @zackburgess1.

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