Dr. David K. Humphreys: Examining the Effects of Stand Your Ground Laws on Public Safety

Safety in Numbers

Welcome to Everytown Research & Policy’s Safety in Numbers blog series, where we will invite leading experts in the growing field of injury and safety prevention to present their rigorous research in clear, user-friendly language on a regular basis. Our goal is to share the latest developments, answer important questions, and stimulate evidence-based conversations on gun violence prevention in which all of us can participate. If you have a topic you want to hear more about, please feel free to suggest it at: [email protected].

Sarah Burd-Sharps, Director of Research

Note: The views, opinions, and content expressed in this post do not necessarily reflect the views, opinions, or policies of Everytown for Gun Safety Support Fund.

Dr. David K. Humphreys was studying alcohol-related violence in the United Kingdom when two things shifted his attention to gun violence in the United States. 

First, he married an American and began spending time in Philadelphia and elsewhere in the US, where he became increasingly familiar with the prevalence of gun violence. Second, spending more time in the US also led to meeting experienced gun violence researchers, such as Dr. Doug Wiebe at the University of Pennsylvania, whose research inspired Dr. Humphreys’ research to take a new direction.

“The prevalence of guns in society struck me: from local news reports of everyday gun violence, active shooter public service posters in public places, visible firearms and military-grade weapons carried by US law enforcement officials, and even handguns in the homes of my new family members,” Dr. Humphreys said. “This all made for a stark contrast with life in Europe.”

Researching gun violence is important to Dr. Humphreys because it ripples across entire communities, harming them socially and economically. His research focuses on Stand Your Ground (SYG) laws. These laws allow people to shoot to kill in public even when they can safely walk away from the danger. His interest in this topic stemmed from the 2012 shooting death of 17-year-old Trayvon Martin. Trayvon Martin’s death, and the court case that followed, put SYG laws in the spotlight. 

“The case and the public’s response to it drew my attention to the ongoing racial inequalities in the US and particularly how the adverse effects of laws and government policies can exacerbate these problems,” Dr. Humphreys said.

Learn more about Dr. Humphreys’ research in his own words:

The topic of who and under what circumstances a civilian can use deadly force is not a recent phenomenon. Over time, many societies have restricted deadly force into fewer hands such as armed forces and police. Some have even argued that this has led to declines in violence. But in the US, unique cultural and historical characteristics have shaped a different legal landscape around these rights than in other countries.

Florida’s SYG law led to a striking increase in gun homicides. 

Florida was the first US state to enact a SYG law in 2005. Ten years after Florida enacted the law, Dr. Wiebe and I started looking at its effect. We collected data on monthly homicide and suicide deaths from 1999 to 2014. Then, we compared homicide deaths before and after enactment of the law to measure any changes to homicide trends. 

The initial findings were striking. Florida’s homicide rates increased by 24 percent and firearm homicide rates by 32 percent following the implementation of the state’s SYG law. We spent several weeks puzzled over these findings. We performed a range of tests and alternative analyses to explain the increase. But to this day, the large increase in Florida’s homicide rates following the law lacks any plausible alternative explanation. 

This led us to think about the impact of similar laws in the 24 other states that had followed Florida’s example. The University of Oxford awarded us a small grant to collect and analyze studies related to SYG laws. The first paper from this study was published in the American Journal of Public Health in March 2021. 

Then, the Joyce Foundation awarded us a larger grant to examine the impact of SYG laws across states and how the impact of these laws has differed. In particular, we want to know whether the effects we found in Florida were an exception to the norm.

States with SYG laws see increases in homicides and other violent offenses.

We found 25 studies examining the impact of SYG laws on homicide, crime, or other legal outcomes. The studies were diverse, using different approaches, data, and statistical modeling strategies. There are three main findings from these studies:

1. There is no evidence that SYG laws increase public safety, as claimed by advocates of the laws.
2. SYG laws are associated with increases in homicides and other violent offenses.
3. Judgments about whether the use of deadly force was lawful are prone to racial bias.

There is growing information on the impact of SYG laws, but there are some aspects that need more research. The current studies compare homicide rates from states with SYG laws to states without the law. Or they compare trends before and after the enactment of SYG in specific states, as we did in our Florida study. This makes it difficult to understand the extent and reach of the harmful effects of SYG laws. We aim to shed light on this question in our upcoming analysis from the Joyce Foundation-funded Stand Your Ground Project.

Research shows that SYG laws have many harmful effects, but states are still trying to pass or expand them.

Research to date suggests that SYG laws have a range of harmful effects, including: 

• increasing death by homicide, including gun homicide;
• increasing non-fatal injuries (which has yet to be assessed); and
• perpetuating racial injustice. 

There is still much to learn about the impact of SYG laws. But none of these findings support SYG laws as beneficial. Yet states—including Ohio, Arkansas, and New Hampshire—have still enacted SYG laws in 2021. We hope our work examining the impact of SYG laws leads to more evidence that will inform these policy decisions.

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About David K. Humphreys

David K. Humphreys, PhD is an Associate Professor of Evidence-Based Intervention and Policy Evaluation at the University of Oxford. He is an interdisciplinary social scientist whose research spans several fields including: criminology, social policy, public health, and epidemiology. His main topic of interest focuses on the causes, consequences and prevention of violence and injury. Much of his research investigates how structural changes—such as laws, regulations or changes to the built and social environment—impact on the rate and/or distribution of harm in the population.