Association of State Firearm Laws With Firearm Ownership and Mortality.

Introduction: Firearm injury is a leading cause of death among Americans. Because the right to bear arms is protected by the Second Amendment, policymakers must consider the impact of legislation on both firearm ownership and firearm harms. The current state of knowledge in firearm research majorly examines the impact of firearm legislation on firearm injuries and fatalities alone, and it relies on correlational analyses. The few studies that consider causal effects employ counterfactual-based inference. This study introduces information-theoretic tools to explore the role of firearm laws in mitigating firearm harms while maintaining citizens' right to bear arms. Methods: The authors study monthly time series from January 2000 to October 2019 for the implementation of firearm laws from RAND's State Firearm Law Database, firearm deaths by intent from the Centers for Disease Control and Prevention databases, and firearm ownership from an econometric model. The authors employ transfer entropy, an information-theoretic method that relies on Granger causality, to infer relationships from time series. Specifically, the authors examine transfer entropy from firearm restrictiveness to deaths per firearm owner, firearm ownership, and firearm deaths, independently. Results: On a national level, the authors uncover a negative association from firearm restrictiveness to deaths per firearm owner and a positive association from firearm restrictiveness to firearm ownership. On a regional level, the authors identify a negative association from firearm restrictiveness to deaths per firearm owner in the Northeast, a negative association from firearm restrictiveness to firearm ownership in the Midwest, and a negative association from firearm restrictiveness to firearm suicides in the South. Conclusions: The authors present an information-theoretic approach to study relationships in firearm research. This method provides preliminary evidence for the role of restrictive legislation in promoting safe firearm ownership. The authors find that firearm acquisition considerably increases after the implementation of restrictive firearm laws, and simultaneously, firearm deaths decrease. These effects vary with respect to death by intent and the geographic region the laws were implemented in.