Laws aimed at preventing child access to guns are effective, reducing self-inflicted firearm injuries and deaths among minors. That was one of the major findings in an exhaustive review released today by the RAND Corporation, a public policy institute. The new report, a follow-up to one published in 2018, assesses the effects of gun laws and provides recommendations to policy makers.

Child-access prevention (CAP) laws allow authorities to criminally charge adults who intentionally or accidentally grant children unsupervised access to firearms. According to a 2018 study, an estimated 4.6 million American children live in homes where at least one gun is unlocked and loaded. Research published in 2019 shows that kids in such homes accounted for three-quarters of all firearm suicides among children between the ages of 10 and 18. Based on research showing that CAP laws protect children, RAND now recommends that states pass these laws if they haven’t already done so, and that they consider making child access to firearms a felony. As of January 2020, 29 states and Washington, D.C., have some form of CAP law in place. Massachusetts has one of the strictest, allowing authorities to charge firearm owners if children under 18 could, potentially, gain access to one.

The new report, a product of RAND’s Gun Policy in America Initiative, which launched in 2016, assessed the impact of 18 kinds of firearm laws on outcomes such as suicide and violent crime. “While there has been limited funding in the space of gun policy research, there really has been a striking increase in studies that have come out in the last few years,” said Rosanna Smart, one of the report’s co-authors. There’s now a “robust body of evidence supporting the effects of some of these laws, particularly on homicide and suicide.”

To determine the impact of the various gun laws, the authors combed through and evaluated 123 studies. If at least three high-quality studies — those that were in some way able to establish cause-and-effect between the law and an outcome — suggested a particular effect, the authors considered the evidence strong enough to warrant policy recommendations, also included in the RAND report.

The report also finds that stand-your-ground laws, which allow individuals to use deadly force in public to protect themselves, increase firearm homicides. As of January 1 of this year, 34 states have these laws or similar ones on the books. These laws are an expansion of the so-called castle doctrine, the principle that people are allowed to use deadly force to protect their home and its inhabitants from intruders. Since the authors found that these laws increase homicide risk, RAND recommends that states with stand-your-ground laws consider repealing them.

The RAND report found that other policies may shape public health outcomes, too, but the strength of the evidence varied. For instance, RAND found moderate evidence to suggest that intimate-partner homicides drop when laws are passed that prevent people from owning guns if they have domestic violence-related restraining orders against them. (The authors deemed evidence “moderate” if at least two studies support a particular conclusion, and no studies contradict it.) The report also found moderate evidence to suggest that background checks reduce firearm homicides and that waiting periods reduce homicides and firearm suicides.

“RAND has done a great deal of work, compiling a lot of studies on the effectiveness of gun laws and carefully assessing the rigor of the studies,” said Daniel Webster, director for the Center for Gun Policy and Research at Johns Hopkins University, who was not involved in the report. He called it “a great resource for those who do gun policy research.” However, Webster said he disagreed with some of the ways in which RAND rated evidence quality and had concerns over the ways in which the authors lumped together certain kinds of laws that could have distinct effects.

The report did not find sufficient evidence to recommend some other gun policies, red flag laws, which allow a judge to remove guns from someone deemed a threat, and firearm safety training. But the lack of evidence does not mean the laws don’t keep people safer; it just means that more high-quality research is needed to determine whether or not they do. “We don’t have enough consistent evidence to support the effect one way or another,” Smart said.

RAND was selective about the types of evidence it considered. It did not consider simple correlational studies — which identify associations between gun laws and specific outcomes — to be evidence for or against a particular policy. For instance, if a study found that states with waiting periods had fewer suicides at one point in time compared with states without waiting periods, the authors would have considered it insufficient evidence that waiting periods reduce the risk of suicide. Correlational studies cannot establish cause-and-effect; states may have fewer suicides for reasons unrelated to waiting periods. To zero in on cause-and-effect, the RAND authors only considered studies to be evidence if they went beyond finding correlations. For the relationship between waiting periods and suicide, for instance, the RAND researchers considered studies that assessed how suicide rates changed after waiting periods were implemented in certain states, but not others.

According to the RAND authors, more and better data is needed to fully assess the efficacy of gun policy in America. But that data isn’t easy to come by. For decades, the U.S. government has underfunded research on gun violence compared with research on other public health issues, like transportation safety. Congress finally appropriated $25 million for firearm research in 2019, but a one-off commitment won’t do enough. Smart said that we need “large scale data infrastructure that is supported continuously over time.”

RAND’s gun work was funded by Arnold Ventures, which also funds The Trace. Here’s where you can read our editorial independence policy and our policy on donor transparency.