Legal Firearm Sales at State Level and Rates of Violent Crime, Property Crime, and Homicides

Abstract
Introduction
The effects of firearm sales and legislation on crime and violence are intensely debated, with multiple studies yielding differing results. We hypothesized that increased lawful firearm sales would not be associated with the rates of crime and homicide when studied using a robust statistical method.

Methods
National and state rates of crime and homicide during 1999-2015 were obtained from the United States Department of Justice and the Centers for Disease Control and Prevention. National Instant Criminal Background Check System background checks were used as a surrogate for lawful firearm sales. A general multiple linear regression model using log event rates was used to assess the effect of firearm sales on crime and homicide rates. Additional modeling was then performed on a state basis using an autoregressive correlation structure with generalized estimating equation estimates for standard errors to adjust for the interdependence of variables year to year within a particular state.

Results
Nationally, all crime rates except the Centers for Disease Control and Prevention–designated firearm homicides decreased as firearm sales increased over the study period. Using a naive national model, increases in firearm sales were associated with significant decreases in multiple crime categories. However, a more robust analysis using generalized estimating equation estimates on state-level data demonstrated increases in firearms sales were not associated with changes in any crime variables examined.

Conclusions
Robust analysis does not identify an association between increased lawful firearm sales and rates of crime or homicide. Based on this, it is unclear if efforts to limit lawful firearm sales would have any effect on rates of crime, homicide, or injuries from violence committed with firearms.