March 5, 2018 – States regulate the buying and selling of firearms and track who purchases them. Strong firearm policy environments have been associated with lower rates of firearm deaths. But firearms can move across state lines and that’s a challenge to effective state policies.

Who and When: State firearm death rates by county from 2010 through 2014 for people who died from firearm suicide and homicide in 3,108 counties in the 48 contiguous United States

What (Study Measures): Each county was given two scores: a state policy score based on the strength of its firearm laws (for example, laws regulating dealers, background checks, licensing, reporting of lost or stolen guns, multiple purchases, and gun design and manufacturing standards) and an interstate policy score where a higher score indicated stricter laws in nearby states; counties were divided by low, medium and high scores (exposures); county-level rates of firearm, nonfirearm and total homicide and suicide, and statistical models comparing groups of counties (outcomes)

How (Study Design): This was an observational study. Researchers were not intervening for purposes of the study and they cannot control all the natural differences that could explain the study findings.

Authors: Elinore J. Kaufman, M.D., M.S.H.P., of New York-Presbyterian/Weill Cornell Medical Center, New York, and coauthors

Results: Strong firearm laws in a state were associated with lower rates of firearm homicide in counties; counties in states with weak laws had lower rates of firearm homicide only when surrounding states had strong laws; strong firearm laws in a state were associated with lower firearm suicide and overall suicide rates regardless of the strength of laws in other states.

Study Limitations: Only a few states have strict laws so the ability to detect an effect of the strictest laws may have been limited; mail and internet commerce may mitigate distance; the laws analyzed cannot completely eliminate gun theft or illegal purchases or differences in law enforcement; other limitations of the data and confounding factors.