Opponents of gun control have frequently pointed to high rates of gun violence in cities such as Chicago to argue that strong state gun control laws are not effective.

But guns used in states with stricter gun laws typically flow from states with weaker laws, according to a new study from Boston University School of Public Health (BUSPH) researchers.

The study, published in the Journal of Urban Health, found the majority of crime guns used in Illinois, Massachusetts, and New Jersey come from other states, while several other states see nearly all of their crime guns purchased in-state. The researchers also found that wait periods, permit requirements, bans on guns for people with histories of a violent misdemeanor, and relinquishment of guns by people convicted of a violent misdemeanor could together decrease a state's in-state crime guns by 13.7 percent.

"This study shows that strong firearm laws are effective in reducing access to guns for potential use in crimes in a state," says study co-author Michael Siegel, professor of community health sciences at BUSPH. "It may be that higher rates of gun violence in some states with strong firearm laws may be not because they have strong laws, but because their neighboring states have weak laws."

Using 2006-2016 data from the Bureau of Alcohol, Tobacco, Firearms, and Explosives, which traces the origin of a sample of guns recovered after use in a crime in the US, the researchers were able to identify what proportion of crime guns came from and were used in each of the 50 states.

The researchers then compared this "import-export" data with information from the State Firearm Law Project, a database tracking 133 gun law provisions covering 14 categories of laws across all 50 states for each year during the study period. Led by Siegel, the project uses detailed definitions of each state law provision, including specific exemptions, to code a state as having or partially having that provision.

The researchers selected eight provisions from the database that might affect the ease of obtaining a gun: a licensing requirement for all gun dealers; a waiting period before the sale of a handgun; a permit requirement for buying a gun; a requirement to register or record every handgun sale; a ban on people with a history of a violent misdemeanor purchasing guns; a requirement for anyone prohibited from possessing a gun to relinquish all guns in their possession; a background check requirement for all gun purchases; and a state criminal offense for buying a gun for someone who is not allowed to buy or possess a gun. The researchers created a gun law index with scores from 0 to 8, based on how many of these laws a state had on the books on average from 2006 to 2016, and on the strength of these laws where and when present.

The index ranged from 0 in 24 states to 6.1 in Hawaii and California. New Jersey, with an index of 5.0, had the lowest percentage of traced in-state crime guns at 22.8 percent, while Indiana, with an index of 1.0, had the highest at 83.8 percent.

Adding controls for state-level gun ownership and production and density of gun dealers, as well as crime rates, degree of urbanization, and other factors, the researchers found a clear association between stronger gun control laws and fewer crime guns originating in a state. Crime guns flowed "from Southeastern states with weak gun laws up the coast to Maryland, New York, and Massachusetts; from Midwestern states with weak gun laws to Illinois; and from Western states with weak gun laws to California," the authors wrote. "While the average gun law index across the primary destination states was 3.3, the average gun law index for the primary source states was 1.4."

As states enacted gun laws during the study period, the researchers saw a decrease in crime guns originating in those states. They also saw an increase in crime guns originating in states that repealed or did not add gun laws during the study period.

The researchers were able to identify which four laws had the biggest impact. A waiting period for handgun purchases reduced in-state crime guns by 1.9 percent, requiring permits to buy a gun by 3.9 percent, prohibiting people convicted of a violent misdemeanor from owning guns by 3.2 percent, and requiring relinquishment of guns when a person becomes disqualified from owning them by 4.7 percent.

"This paper provides evidence that policy makers can now use in deciding what approaches to take to try to keep guns out of the hands of people who are at a high risk to commit crimes," Siegel says. "It also shows that if states fail to act, they may actually be endangering the lives of residents of nearby states."

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The study was supported by a grant from the Robert Wood Johnson Foundation's Evidence for Action Program.

About Boston University School of Public Health:

Boston University School of Public Health, founded in 1976, offers master's- and doctoral-level education in public health. The faculty in six departments (biostatistics; community health sciences; environmental health; epidemiology; global health; and health law, policy & management) conduct policy-changing public health research around the world, with the mission of improving the health of populations--especially the disadvantaged, underserved, and vulnerable--locally, nationally, and internationally.