Debate over the value of tough state gun control laws has reached a fever pitch following last month's deadly shooting of 17 people at a Florida high school.
Now, results from a new study indicate that such laws are potentially so effective they can prevent firearm-related murders on a regional basis, with the benefits extending into other nearby states that have more lax laws on the books.
States with strong firearm laws have overall lower rates of gun-related murder and suicide, according to the county-by-county analysis.
But counties in states with weak gun laws also appear to gain some protection from gun violence if they are located next to states with stronger laws, researchers reported.
"We found that in states with relatively lenient laws, if the surrounding states had stricter laws we found a lower firearm homicide rate," said study author Dr. Elinore Kaufman, a trauma surgeon at New York-Presbyterian Weill Cornell Medical Center in New York City. "This indicates there might be a protective effect that extends across state lines."
Firearms now account for more than 50 percent of suicides and two-thirds of homicides in the United States, the researchers said in background notes.
Despite this, gun control laws are enacted mainly at the state level, and varying laws across a region could complicate an individual state's efforts to tackle the issue of gun violence, the researchers said.
Kaufman and her colleagues analyzed gun control laws across the continental United States, and assigned each county a state-level and interstate-level score reflecting the strictness of firearms laws.
The state-level score focused solely on gun laws in that state, while the interstate score took into account the gun laws of states near each county.
"Our concept was that state borders are permeable," Kaufman said. "We need to look beyond them when we're looking at the effect of firearms laws. Guns, like any other consumer good or product, can move across state lines quite easily."
The policy scale assessed firearms law strength based on six categories—gun dealer regulation; background checks for private sales; license requirements to purchase or own guns; "junk gun" regulations that limit or ban sales of cheap handguns; reporting requirements for lost or stolen guns, and restrictions on the number of gun purchases a person can make within a given time frame.
The researchers then compared the relative effectiveness of state gun control laws against data from the U.S. Centers for Disease Control and Prevention on firearm suicide and homicide deaths for just over 3,000 counties in the lower 48 states.
The investigators found a clear relationship between gun control and firearm suicide rates. States with weak gun laws had gun-related suicide rates as much as 43 percent higher than states with strong laws.
Individual counties did not appear to gain any suicide-prevention benefit from being located near a state with strong gun laws, the researchers reported.
But when it came to murder, the effects of one state's strong gun legislation appear to ripple across the surrounding region.
The presence of nearby states with tough gun laws cut by half the relative firearm-related murder rate of counties located in states with weak gun control laws, the researchers found.
Counties near states with strong gun laws had an 18 percent higher relative rate of firearm murders, compared with a 38 percent higher relative rate for counties nestled in a region with lax gun laws, the results showed.
The study was published online March 5 in the journal JAMA Internal Medicine.
"It tells us that there's a suggestion that having a little more fierce regulation may assist in minimizing gun violence and gun-related suicide," said Dr. Stephen Cohn, trauma medical director for Staten Island University Hospital in New York City.
Strong gun control laws might reduce the general availability of firearms across a region, Kaufman said.
"We need to look beyond state borders when we're looking at the effect of firearms laws," she concluded.
On top of the gun control laws considered in this study, states also should consider age restrictions on firearm use and ownership, said Dr. Rex Archer, director of health for the City of Kansas City, Mo.
"We know from brain development with impulse control, it's really not until after age 25 that you should be having a gun unless you're under supervision," Archer said. "Until you're older than that, the brain in humans just hasn't gotten to that point of being able to control impulses and not react on something without thinking about the long-term consequences."
More information: Elinore J. Kaufman et al. State Firearm Laws and Interstate Firearm Deaths From Homicide and Suicide in the United States, JAMA Internal Medicine (2018). DOI: 10.1001/jamainternmed.2018.0190
Journal information: JAMA Internal Medicine
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