Panelists at a Penn LDI virtual seminar explained why there isn’t enough evidence to fully understand what works and what doesn’t in the field of gun violence prevention. The LDI event was co-sponsored by the Penn Injury Science Center.

Efforts to address the rising public health crisis of firearm violence are being stymied by the lack of scientific evidence about which current laws and proposed policies are–or are not–effective interventions. That’s according to a May 3 virtual seminar of top experts convened by the University of Pennsylvania’s Leonard David Institute of Health Economics (LDI) and co-sponsored by the Penn Injury Science Center.

Therese Richmond, PhD, RN

As she opened the session, Therese Richmond, PhD, RN, moderator, LDI Senior Fellow, Penn School of Nursing Professor, and Research Core Director at the Penn Injury Science Center cited the latest annual count of U.S. firearm carnage: more than 26,000 suicides by gun, 20,000 homicides, 549 unintentional shootings, and 995 other firearm deaths. That’s roughly 1 person killed by gun every 11 minutes around the clock, every day.

Primary Cause of Children’s Death

And there are some particularly tragic inequities within these statistics. Rates of firearm homicides are 11-fold greater for Black males than white males. And more children and adolescents aged 1-19 years die annually from firearm injuries than from any other single cause.

Scientists have been investigating gun violence as a public health hazard for a long time but that suddenly stopped in 1996 as the gun lobby partnered with its supporters in Congress to pass the Dickey Amendment that blocked the Centers for Disease Control and Prevention (CDC) from funding any research “to advocate or promote gun control.”

Twenty-three years later, in 2019, Congress lifted those prohibitions and from 2020 to 2022, the CDC and National Institutes of Health (NIH) awarded more than $149 million in research grants related to firearm injury prevention research. And while this new infusion of money and research effort is moving forward, there are still very large evidence voids in the scientific understanding of how any given law or potential intervention actually works to decrease or not decrease gun violence.

Richmond, a board member of the Research Society for the Prevention of Firearm-Related Harms, discussed current research evidentiary needs with three seminar panelists who are also board members in that same Society. They are Andrew Morral, PhD, Senior Behavioral Scientist and Director of the National Collaborative on Gun Violence Research at the RAND Corporation; Joseph Richardson, Jr., PhD, who leads the Prevent Gun Violence: Research, Empowerment, Strategies & Solutions (PROGRESS) initiative and is Executive Director of the Transformative Research and Applied Violence Intervention Lab at the University of Maryland; and Ali Rowhani-Rahbar, MD, PhD, Director of the Firearm Injury & Policy Research Program at the University of Washington.

Convoluted Gun Laws

The world of state guns laws is convoluted. The number of laws is so extensive and varied that no one appears able to estimate it. There are around 20 major classes of state firearm laws, with numerous subcategories within each class. Examples of these classes include background check laws, child-access prevention laws, concealed-carry laws, and laws regulating the storage and use of firearms. Regulations vary significantly by state as they cover aspects such as permits for purchase and possession, firearm registration, concealed and open carry regulations, restrictions on certain types of firearms and magazines, and various self-defense laws like the “castle doctrine” or “stand-your-ground” laws.

Andrew Morral, PhD

Richmond noted that the news media and public debate about gun violence tend to focus on federal policy even though few of the individual states’ gun laws have been evaluated. She asked Morral to provide a synopsis of RAND’s extensive reviews of state laws as well as the academic literature about them.

“There’s a lot of correlational evidence of some association between the laws states pass and the outcomes they achieve in terms of firearm homicide, suicides, and injuries,” said Morral. “You can say, ‘Hawaii, California, New York, and New Jersey have particularly low firearm suicides and homicide rates and they also happen to be the states that have particularly restrictive gun laws.’ But that’s not good enough to make a claim about what is driving those outcomes. They’re different from other states in a lot of ways. They’re blue states and they’re wealthy states. How do you know it’s not just the wealth that’s leading to this difference? My group at RAND’s Gun Policy in America project has been working for eight years to tease apart what can be attributed to the law versus what might be attributable to other aspects of a state.”

Latest Analysis

“For the most part,” Morral continued, “state laws haven’t been studied carefully but that has been changing, and we have been updating our systematic review, going through thousands of articles to identify those that use more rigorous methods of identifying the effects of gun laws. We have sorted the policies that have been studied into these different categories of levels of evidence, our highest level being what we call ‘supportive evidence’ that is comprised of multiple studies demonstrating a particular effect.”

He indicated that RAND rates three types of state gun laws as having supportive evidence for various kinds of results in the scientific literature:

RAND’s second, lower-quality level of evidentiary ratings indicate that background checks, minimum age purchase laws, and firearms surrender laws help to reduce firearm homicides–this last particularly so in domestic violence cases.

However, Morral emphasized that states that have laws like firearm surrender statutes often don’t enforce them. Technically, judges may be required by law to ask whether a domestic offender has firearms but fail to do so. He pointed to a recent study in North Carolina suggesting that in a large proportion of cases, that despite being required by law to do it, judges there simply don’t inquire about an offender’s firearms.

“So,” Morral said, “you wouldn’t expect a firearms surrender law to have as much effect in North Carolina as it does in another state where the judges are doing what they’re supposed to do. And this is hard to study because getting data on implementation fidelity is really hard. That is an information collection effort where you send people out into the field to collect that data, and that’s expensive.”

Ali Rowhani-Rahbar, MD, PhD

Social Determinants and Firearm Violence

Looking beyond just the legal language and politics of gun control laws, Richmond asked if firearm violence was looked at as one of the social determinants of health, how could other kinds of public policies affect firearm violence rates?

Rowhani-Rahbar said there was a recent scoping review of the literature that found very few studies that have empirically looked at the relationship between societal and structural level determinants of these firearm violence outcomes. A couple of studies of redlining showed how those historic racist policies are associated with those very same neighborhoods that are now experiencing higher levels of gun violence.

He noted that several studies have focused on state social policies’ impact on total crime or total violence and suicide but not explicitly with firearm-related outcomes.

“I think that’s really important because while different forms of violence are interconnected and have shared risk and protective factors, the pathways for firearm-related violence are not necessarily identical to those for non-firearm-related violence. There is obviously a need to examine the impact of state social policies on firearm-related outcomes,” Rowhani-Rahbar said.

“We did a scoping review of income support policies on firearm-related death, and we found four studies globally on that, one from Brazil and three from the United States,” Rowhani-Rahbar said. “Most of these are cash transfer programs. Some of the evidence is that there seems to be an association between those policies and reduction in firearm-related death and injury. A recent study looked at state minimum wage policies and firearm-related homicide that showed an association between minimum wage and reduction in firearm homicide. Another looked at state social spending and food insecurity in relation to firearm related suicide. They showed significant reductions in firearm-related suicide.”

Hospital-Based Violence Intervention

Panelist Richardson is heavily involved in a related area of research focused on how community-based violence intervention (CVI) programs and hospital-based violence intervention programs (HVIPs) can be used in ways that reduce firearm-related harms in a community.

Joseph Richardson, Jr., PhD

Richardson explained, “My mentor, Carnell Cooper, MD FACS, who started one of the first HVIPs programs at the University of Maryland, conducted one of the first studies to test the effectiveness of the concept and found that among the treatment group, the reinjury rate was 5% compared to the non-treatment group, which was 36%. So at least in his study, he was able to show that these programs are effective in terms of providing behavioral health and social services primarily for young Black men who are disproportionately impacted by gun violence. The program provided the patients with behavioral health and social services, including cognitive behavioral therapy, to not only reduce their rate of trauma recidivism, but also criminal recidivism as well, and get them back into employment and educational opportunities.”

“My colleague and I, Daniel Webster, ScD, have conducted a systematic review of HVIPs,” Richardson continued. “And what we found is that there were really no conclusive results. There are pieces of programs that are effective, but in total, we did not find conclusively that there were enough studies to say that these programs are totally effective in reducing trauma, recidivism, and other metrics that we use to gauge success.”

“I think part of that involves the lack of experimental designs for HVIPs,” said Richardson. “Also, there are challenges with increasing the sample size. For example, in the study conducted by Dr. Cooper at the University of Maryland, there were 100 participants in that study, but it took 33 months to get those 100 participants. So, we often find challenges with recruitment and retention. Then there’s also the challenge of determining what aspects of the programs actually work because not all HVIPs are the same. For my program—we were the first fully operational program in the Washington, D.C. metro area—we had 116 participants over a three-year period. And over that period, we had one person come back to the hospital for a violent injury. So, numerically, we were successful, but we still cannot prove what aspects of the program contributed to that significant reduction in trauma recidivism. We need more research to understand what that looks like, and also the ways that HVIPs programs connect with street outreach programs.”

Looking Ahead

As the session ended, Richmond asked the panelists for a final comment identifying one promising policy area that they want to see move forward, or see new evidence emerge in that reduces firearm violence? These are their answers:

Morral: “The low hanging fruit politically and possibly empirically, is removing firearms from people who are prohibited possessors. There’s a huge number of people in the country who are prohibited possessors and have firearms but there’s no general mechanisms for identifying them or having them give up their firearms. We know that most firearm crime is committed by people who are prohibited possessors. Many gun owners say we don’t need more gun laws, we just need to enforce the laws, and this would, I think, fit into that enforcement framework.”

Rowhani-Rahbar: “I propose policies that strengthen our communities in terms of overcoming economic stress and hardship that could, in the long term, have some sizable impact in those communities.”

Richardson: “Change the policies related to felony disenfranchisement and the collateral consequences. We’ve seen the impact a felony has on the outcomes of people who are coming back from prison and trying to penetrate the legal labor market. Their felony record punishes them for a lifetime. Often, these are young men who are disadvantaged by that record and revert back to crimes of economic survival, which probably contributed to their engaging in firearm violence from the outset.”


Hoag Levins

Editor, Digital Publications

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