Guns are the third leading cause of injury-related death in the country. Every year, nearly 12,000 gun homicides happen in the U.S., and for every person killed, two more are injured. Whether Congress will do anything about this violence is a whole other (depressing) article. But there is evidence that change is possible.

Last year, a study published in Epidemiologic Reviews “systematically” reviewed studies examining the links between gun laws and gun-related homicides, suicides and unintentional injuries and deaths. Researchers eventually gathered evidence from 130 studies in 10 countries, finding that in certain places, gun restrictions are associated with declines in gun deaths. For instance, laws that restrict gun purchasing, such as background checks, are associated with lower rates of intimate partner homicide; while laws addressing access to guns, such as safe storage policies, are associated with lower rates of unintentional gun deaths among children. Study co-authors Julian Santaella-Tenorio, Magdalena Cerdá, Andrés Villaveces and Sandro Galea write:

This heterogeneity in approaches and implementation methods makes it critical to identify approaches that are less likely to be effective and to identify which strategies, looking forward, may be more likely to work. In addition, examining the associations between specific policies and firearm-related deaths across countries can improve our understanding about which types of laws are more likely to be successful in reducing firearm mortality rates in similar contexts or within diverse legal frameworks.

The study’s findings are a mixed bag — some of the gun laws studied seemed to reduce gun deaths, while others seemed to make no difference or increase deaths. For example, a number of studies examined found no association between concealed carry laws and gun homicides in the U.S. However, one study using injury data from southern Arizona found higher proportions of firearm injuries and deaths associated with concealed carry. Yet another study in Colombia examined the effects of laws banning the carrying of guns during weekends after paydays, holidays and elections days in two Colombian cities, Cali and Bogota. That study found a 14 percent reduction in homicide rates in Cali during no-carry days and a 13 percent reduction in Bogota.

Studies on background checks and waiting periods came in mixed as well. For example, one study cited found no association between waiting periods and homicides and suicides. On the other hand, researchers have found that gun purchase bans for people with certain mental health conditions were associated with fewer homicides. One study found more stringent background checks were linked with fewer gun homicides. States with laws banning people with domestic violence restraining orders from owning and purchasing a gun also experienced reductions in intimate partner homicide. But one study found no homicide effect for laws that restricted gun access among those convicted of domestic violence.

Two cross-sectional studies analyzed found that gun permits and licenses were associated with lower rates of gun suicide. In Missouri, researchers studied the effect of repealing requirements that people need a valid license to buy a gun, finding the repeal was associated with a 25 percent increase in homicide rates. On laws regulating gun storage, one study found that such child access prevention laws were associated with fewer unintentional gun deaths among children younger than 15, but not among older teens. Another found child access laws were linked to a reduction in all suicides among people ages 14 to 17. A study using hospital discharge data found that such storage laws were associated with lower nonfatal gun injuries among those younger than 18.

The Epidemiologic Reviews study included research on particular laws as well. For example, a study on the U.S. Gun Control Act of 1968 — which restricted the sale of so-called Saturday night specials, among many other measures — did not find associated changes in homicide rates. But a study on Washington, D.C.’s 1976 law banning ownership of automatic and semiautomatic firearms and handguns found an “abrupt” reduction in homicide and suicide rates. Globally, Australia’s 1996 National Firearms Agreement, which banned certain kinds of firearms, was linked with a significant reduction in gun death rates. In addition, Australia has not experienced a mass shooting since the law was enacted. Control gun laws in Brazil, Austria and South Africa were also associated with fewer gun deaths.

Overall, researchers were able to identify some “general observations” in combing through the 130 studies — most notably finding that the simultaneous enactment of laws targeting multiple gun regulations were associated with fewer gun deaths in certain countries. Another big finding: we simply need more research to understand what works and what doesn’t to prevent gun deaths. The researchers also noted that few studies have delved into the impact of gun safety laws on particular populations or whether such laws affect social attitudes, norms and behaviors. The authors write:

To conclude, we have provided an overview of national and international studies on the association between firearm-related laws and firearm injuries/deaths. High-quality research overcoming limitations of existing studies in this field would lead to a better understanding of what interventions are more likely to work given local contexts. This information is key for policy development aiming at reducing the burden posed to populations worldwide by violent and unintentional firearm injuries.

In more recent gun research, a study published this month in Health Affairs set out to quantify the clinical and economic burden associated with emergency room visits for gun-related injuries in the U.S. Researchers examined data from the Nationwide Emergency Department Sample, identifying 150,930 people between 2006 and 2014 who showed up to an ER alive, but with a gun-related injury. That number represents a weighted estimate (that’s a fancy term for adjusting data to represent the greater population) of 704,916 patients.

ER visits for gun injuries was lowest among those younger than 10 and highest among ages 15 to 29. Incidence of gun injury was about nine-fold higher for male patients — among men ages 20 to 24, more than 152 patients per 100,000 visited the ER for a gun injury. Most of the patients had been injured in an assault or unintentionally. The proportion injured in an attempted suicide was more than two-fold higher among Medicare beneficiaries. Handguns were the most common cause of the injury, followed by shotguns and hunting rifles.

Among the more than 150,000 cases of gun injury at the ER, 48 percent were discharged home, 7.7 percent were discharged to other care facilities, about 37 percent were admitted to the hospital and just more than 5 percent died during their ER visits. Overall, 8.3 percent of the gun injury patients either died in the ER or as an inpatient. The average charge for gun injury in the ER was about $5,250; the average charge for those admitted was more than $95,000. Over the entire study period, gun-related injuries cost $2.9 billion in ER charges and $22 billion in inpatient care.

Authors of the Health Affairs study also pointed out the need for more research, citing a 1996 federal measure known as the Dickey Amendment that said injury research funds at the Centers for Disease Control and Prevention could not be used to advocate or promote gun control. Co-authors Faiz Gani, Joseph Sakran and Joseph Canner write:

Researchers, politicians and government officials must work together to ensure that research funds are allocated to promote the understanding of the complex interplay between social, economic and medical factors associated with firearm-related injuries. Only through the adoption of an evidence-based public health approach can the resulting substantial medical and financial burden be reduced.

To request a full copy of the ER study, visit Health Affairs. For a copy of the gun policy study, visit Epidemiologic Reviews.

Kim Krisberg is a freelance public health writer living in Austin, Texas, and has been writing about public health for 15 years. Follow me on Twitter — @kkrisberg.