State gun laws may help curb violence across state lines: study

Results of the study appear in the journal Epidemiology, and are based on an analysis of county-level data on firearm homicides as they relate to state gun laws between 2000 and 2014.

Around 14,000 Americans civilians die and over 75,000 people are treated in emergency departments because of gun violence every year. This study adds evidence that the count and composition of states' gun laws affect within-state homicide incidence. The associations are strongest for background checks compared to other gun laws, including child access prevention laws, dealer registration laws, and licensing laws. As well as examining within-state effects, the research is one of the few studies to explore the potential effects of gun laws on homicides in neighboring states, with the results emphasizing that firearm laws spill over state lines.

The study found that homicide incidence was greatest in counties with weak within-state laws and where the largest nearby population centers were in other states that also weak laws. As an example, the researchers contrast New Hampshire and Alabama, which both had 10 gun laws in 2014. The most populous urban center near New Hampshire is Boston, which had 100 gun laws, whereas the major city nearest to Alabama is Atlanta, where there were 6 laws. The weak gun laws in Alabama and Georgia both contribute to higher homicide incidence in Alabama, but the stronger gun laws in Massachusetts temper the effect of the weak laws in New Hampshire. To explain these results, the researchers suggest it may be easier for guns to flow undetected into places where laws are already weak.

"Gun violence is a public health crisis in the United States," says first author Christopher Morrison, PhD, Assistant Professor of epidemiology at the Columbia Mailman School. "Research has demonstrated that strong gun laws can reduce this burden. It's now becoming clear that weak gun laws don't only drive up gun violence within their own borders, they also affect gun violence in neighboring states."

Study authors include Christopher N. Morrison; Elinore J. Kaufman and Douglas J. Wiebe of the University of Pennsylvania; and David K. Humphreys of the University of Oxford.

The study was supported in part by the National Institute on Alcohol Abuse and Alcoholism of the National Institutes of Health (AA026327).