Assessment of county-level proxy variables for household firearm ownership.

Our objective in this study was to evaluate how well proxy variables for firearm ownership used in county-level studies measure firearm ownership. We applied Bayesian spatial smoothing methods to calculate county-level estimates of household firearm ownership using Behavioral Risk Factor Surveillance System (BRFSS) data (2013-2018). We compared these estimates to four proxies for county-level firearm ownership: the proportion of suicides that were firearm suicides, the average of the proportion of suicides that were firearm suicides and the proportion of homicides that were firearm homicides, gun shops per capita, and federal firearm licenses per capita. U.S. counties for which BRFSS data on household firearm ownership were collected and available for release (n = 304) were included. The median (interquartile range) prevalence of household firearm ownership was 46.6% (37.2%, 56.4%). The per capita rate of federal firearm licenses was most strongly correlated with household firearm ownership (r = 0.70; 95% CI: 0.63, 0.75) followed by the proportion of suicides that were firearm suicides (r = 0.45; 95% CI: 0.36, 0.54). These correlations were stronger among counties with populations of ≥250,000 people. The per capita rate of federal firearm licenses was the best proxy variable for firearm ownership at the county level, however, a better proxy should be identified.