Firearm laws and illegal firearm flow between US states.

Abstract

Considerable variation in firearm legislation exists. Prior studies show an association between stronger state laws and fewer firearm deaths. We hypothesized that firearms would flow from states with weaker laws to states with stronger laws based on proximity and population. Crime gun trace data from 2015 to 2017 was accessed from the Bureau of Alcohol, Tobacco, Firearms and Explosives and compared with the count and composition of firearm legislation in 2015 among the contiguous 48 states. Additional independent variables included population, median household income, distance, and presence or absence of a shared border. We used Exponential Random Graph Models to identify predictors of traced firearm transfers between origin and destination states. After controlling for network structure, firearm laws in origin states were associated with fewer traced firearm transfers (incidence rate ratio [IRR], 0.88; 95% confidence interval [CI], 0.83-0.93; p < 0.001). Conversely, more firearm laws in destination states were associated with more traced firearm transfers (IRR, 1.10; 95% CI, 1.06-1.15; p < 0.001). Larger population at the origin was associated with increased transfers (IRR, 1.38; 95%CI, 1.27-1.50; p < 0.001), as was larger population at the destination state (IRR, 1.45; 95% CI, 1.35-1.56; p < 0.001). Greater distance was associated with fewer transfers (for each 1,000 km; IRR, 0.35; 95% CI, 0.27-0.46; p < 0.001), and transfers were greater between adjacent states (IRR, 2.49; 95% CI, 1.90-3.27; p < 0.001). State firearm legislation has a significant impact on gun trafficking even after controlling for network structure. States with stricter firearm legislation are negatively impacted by states with weaker regulations, as crime guns flow from out-of-state. Epidemiologic, level III.