Five state firearm laws were associated with lower county-level firearm-related suicide rates in a recent analysis, with larger reductions observed in states where more of the laws were in place.
Investigators analyzed annual data from 637 US counties from 2000 to 2023, encompassing 10,893 county-year observations. The counties represented 74% of the US population in 2023. Using county-level suicide data from the Centers for Disease Control and Prevention WONDER database, the investigators applied a difference-in-differences panel model with year and county fixed effects and accounted for multiple county- and state-level factors associated with suicide rates. The primary outcomes were annual county-specific total, firearm- and nonfirearm-related suicide rates.
Among eight state firearm laws examined, five remained statistically significant across sensitivity analyses using 1-, 2-, and 3-year lags. Firearm-related suicide rates at 2 years were 14% lower with violent misdemeanor prohibitions, 9% lower with both a minimum age of 21 years for handgun purchases and laws allowing law enforcement to petition courts for extreme risk protection orders, 8% lower with child access protection laws, and 7% lower with handgun purchase permit requirements.
The investigators found a progressively stronger inverse association as the number of these five laws increased. Compared with counties in states with none of the laws, firearm-related suicide rates were 5% lower when one or two laws, 12% lower with three or four laws, and 29% lower with all five laws. The investigators described a “monotonic pattern of increasing reductions” as the number of enacted laws increased.
In the negative-control analysis, the five laws were not significantly associated with nonfirearm-related suicide rates. The results were confirmed in a sensitivity analysis accounting for serial autocorrelation.
Not all firearm laws showed consistent associations. Waiting-period laws were associated with a 9% lower firearm-related suicide rate at the 2-year lag, but the association was no longer statistically significant at 3 years. Concealed carry permit requirements and “may issue” laws giving law enforcement discretion in approving concealed carry permits were not significantly associated with firearm-related suicide rates at the 2-year lag.
The study had several limitations. Because of its observational design, the investigators could not establish causality or rule out reverse causality. States also tended to enact multiple firearm laws together, making it difficult to isolate the association attributable to any single law. The analysis included only counties with at least 10 reported suicides in a year and at least 18 years of available data, disproportionately excluding smaller rural counties and potentially limiting generalizability to rural areas. Gaps in the data prevented the investigators from using procedures designed to formally assess the parallel-trends assumption in staggered difference-in-differences analyses.
“[F]uture research should employ multilevel modeling to confirm these findings,” wrote lead study author Carolina De Sousa Lima Azevedo, BA, of the Department of Public Health and Community Medicine at the Tufts University School of Medicine, and colleague.
Full disclosures of the study authors can be found in the study.
Source: JAMA Network Open
