Synopsis: Increasing firearm ownership, measured by gun shops per 100,000 people, is linked with higher homicide rates in Trump counties (left chart), but not in Clinton counties.
Chart: The charts display the relationship between “gun shops per 100,000 people” (x-axis) and “homicides per 100,000 people” (y-axis) for Red (left) and Blue (right) counties in the United States. The area of each bubble is proportional to county population (maximum area linked to maximum population in each chart). Each bubble’s color is proportional to the 2016 Presidential election result for each county: dark-to-light red indicates solid-to-marginal Trump majority, dark-to-light blue indicates solid-to-marginal Clinton majority.
Analysis: There is a moderately strong relationship between gun ownership and homicide in Republican counties, but not Democrat counties. Although we do not have county-level gun ownership rates, we do know the number of gun shops in each county (courtesy of the Bureau of Alcohol, Tobacco, Firearms and Explosives; ATF) and can therefore calculate gun-shops-per-100,000-people. This is likely a good proxy for firearm demand, which is likely a good proxy for gun ownership rates.
More guns leading to more homicide is not surprising (Red counties). The lack of a relationship for Blue counties could, perhaps, be explained by gun-shops-per-person being a poor proxy for high-homicide counties where guns are “imported.”
Methodology: Gun shop data were sourced from the ATF1 and homicide data from the County Health Rankings & Roadmaps program2. Election data were taken from Secretary of State websites for each state. County population data were taken from ESRI3. The data were compiled and visualized using custom VBA code in Microsoft Excel4.