In 2005, Florida legislators passed the nation’s first “Stand Your Ground” law, expanding legal immunity for residents to use lethal force when they believe they’re being threatened. A decade later, a new study finds that Florida has experienced a significant increase in homicides, while states without such laws have not.
“From a public health perspective, we were shocked that in a given area, rates of people dying changed so abruptly and in such a sustained way,” study co-author Douglas Wiebe, an associate professor of epidemiology at the University of Pennsylvania Perelman School of Medicine, told me. “These are people dying who otherwise wouldn’t have died. That is what is most profound about our findings.”
Published earlier this week in JAMA Internal Medicine, the study found that in the law’s wake, Florida’s monthly homicide rate experienced an “abrupt and sustained” increase of nearly 25 percent, while the monthly rate of homicide by firearm went up more than 31 percent. No change in overall homicide rates or firearm-related homicide rates were found in the four comparison states — New York, New Jersey, Ohio and Virginia — that don’t have Stand Your Ground laws. In fact, researchers found that in the handful of years prior to implementing the law, Florida had been experiencing a slight decline in monthly rates of homicides. Following implementation of the law, both homicide rates and homicides by firearm increased in the Sunshine State.
“I think we have strong and sufficient evidence to suggest that we should consider repealing this law because it seems to have produced an increase in homicides,” said Wiebe, who also serves on the Executive Committee of Penn’s Injury Science Center. “We should also now go and rigorously evaluate what’s happening in other states (that adopted similar laws), but we don’t need to wait until then to consider acting in Florida.”
According the study, Florida’s Stand Your Ground law “increased the scope of self-defense claims by creating a ‘no duty to retreat’ rule when individuals ‘reasonably believed’ that force was necessary to prevent harm to themselves or others.” While residents already had the right to not retreat if threatened in their own homes, Florida’s new law extended the “no duty to retreat” rule to the public sphere. In fact, the Florida law allows residents to use lethal force even if the shooter is the one who instigated the confrontation that led to him or her feeling threatened. The law also made it legal to use lethal force in defense of property, such as stopping a car theft. To date, 23 other states have adopted a Stand Your Ground law as well.
So, why are Wiebe and his fellow researchers so confident in the association between the expanded self-defense law and Florida’s homicide increase? It’s all in the study design. They used 15 years’ worth of data from the Wide-Ranging Online Data for Epidemiologic Research portal at the Centers for Disease Control and Prevention, gathering monthly data on Florida homicide rates from 1999 to 2014. They examined that data using an interrupted time series design — a design in which an intervention, in this case the enactment of Stand Your Ground, occurs at a specific point in time and so researchers can more confidently compare before-and-after data. The study authors also took into account cyclical trends in homicides rates that typically correspond to certain seasons and months, and they picked a handful of control states without Stand Your Ground laws for comparison purposes.
The result? A large effect on gun homicides across population groups — “it was consistent across the board,” Wiebe said. The study found increases in homicides in all demographic groups, though the effect wasn’t evenly distributed. In particular, enactment of Florida’s Stand Your Ground law was associated with a nearly 29 percent increase in overall homicides among whites; a 20 percent increase among blacks; a nearly 32 percent increase among people ages 20 to 34; a nearly 14 percent increase among people ages 35 and older; a 28 percent increase among males; and a more than 13 percent increase among females. Similar trends were found for gun-related homicides. (When you look at the graphs included in the study, the homicide increases are immediately apparent. For both overall homicides and gun-related homicides in Florida, there’s an abrupt and large spike in 2005 when Stand Your Ground became law.)
Researchers also found no significant changes in homicide rates or gun-related homicide rates in comparison states during the same time period. Still, the researchers wondered: Did anything else happen during that time period that could have so abruptly impacted Florida’s homicide rate? Perhaps, it was related to the economy and the Great Recession. So, said Wiebe, they examined Florida’s suicide rate — a rate that’s typically sensitive to economic and social trends — and could offer a clearer picture of possible contributors to the increased homicide rate. The results: no changes in Florida’s suicide rate between 2005 and 2014.
Wiebe and study co-authors David Humphreys and Antonio Gasparrini write: “Our findings support the hypothesis that increases in the homicide and homicide by firearm rates in Florida are related to the stand your ground law.”
“We were surprised,” Wiebe told me. “We tested this possibility because the scenario suggests this could happen. But you go into this kind of research thinking it’s a bit of a long shot to find evidence of these possibilities. So it was genuinely surprising to see such a large, abrupt and sustained shift. …It’s not often you see such compelling and strong evidence as this.”
Wiebe noted that this is the first study to examine the impact of a Stand Your Ground law using such rich and complex data spanning so many years. However, he said he’s also not surprised it’s the first, considering the dearth of funding for such research. He said this study, which required “an enormous amount of effort,” was done without the support of funding.
“This is a medical, public health and criminal justice problem happening in an area of interest for which there is very little funding available to learn more,” Wiebe said. “This study suggests we need more research dollars at the federal level to support this kind of work.”
For a full copy of the new study, visit JAMA Internal Medicine.
Kim Krisberg is a freelance public health writer living in Austin, Texas, and has been writing about public health for nearly 15 years.