Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2021 Jan;32(1):36-45.
doi: 10.1097/EDE.0000000000001262.

Firearm Homicide Incidence, Within-state Firearm Laws, and Interstate Firearm Laws in US Counties

Christopher N Morrison  1   2 , Elinore J Kaufman  3 , David K Humphreys  4 , Douglas J Wiebe  5
Affiliations

Firearm Homicide Incidence, Within-state Firearm Laws, and Interstate Firearm Laws in US Counties

Christopher N Morrison et al. Epidemiology. 2021 Jan.

Abstract

Background: Firearm homicides occur less frequently in US states with more firearm control laws. However, firearms are easily transported across state lines, and laws in one location may affect firearm violence in another. This study examined associations between within-state firearm laws and firearm homicide while accounting for interference from laws in other nearby states.

Methods: The units of analysis were 3,107 counties in the 48 contiguous US states, arrayed in 15 yearly panels for 2000 to 2014 (n = 46,605). The dependent measure was firearm homicides accessed from the Centers for Disease Control and Prevention (CDC) Compressed Mortality Data. The main independent measures were counts of firearm laws and the proportion of laws within categories (e.g., background checks, child access prevention laws). We calculated these measures for interstate laws using a geographic gravity function between county centroids. Bayesian conditional autoregressive Poisson models related within-state firearm laws and interstate firearm laws to firearm homicides.

Results: There were 172,726 firearm homicides in the included counties over the 15 years. States had between 3 and 100 firearm laws. Within-state firearm laws (incidence rate ratio [IRR] = 0.995, 95% confidence interval [CI] = 0.992, 0.997) and interstate firearm laws (IRR = 0.993, 95% CI = 0.990, 0.996) were independently associated with fewer firearm homicides, and associations for within-state laws were strongest where interstate laws were weakest.

Conclusions: Additional firearm laws are associated with fewer firearm homicides both within the states where the laws are enacted and elsewhere in the United States. Interference from interstate firearm laws may bias associations for studies of within-state laws and firearm homicide.

PubMed Disclaimer

Conflict of interest statement

Conflicts of Interest: None declared

Figures

Figure 1.
Figure 1.
Total counts of within-state firearm laws; 2000–2014. Y-axis represents law counts; x-axis represents years.
Figure 2.
Figure 2.
Total counts of within-state and interstate firearm laws for 2000. This procedure was repeated for each year. Illinois and California have many laws and are marked in blue in the within-state map, but they are surrounded by states with few laws, so they are red in the interstate map.
Figure 3.
Figure 3.
Linear combinations of maximum and minimum observed values and parameter estimates for associations between within-state firearm laws and incidence of firearm homicide. Figure 3a shows predicted association for Model 1. Figure 3b shows the predicted association for Model 2 stratified by the maximum and minimum observed values of the interstate firearm laws.
See this image and copyright information in PMC

Comment in

  • Guns, Laws, and Causality.
    Goin DE, Rudolph KE. Goin DE, et al. Epidemiology. 2021 Jan;32(1):46-49. doi: 10.1097/EDE.0000000000001261. Epidemiology. 2021. PMID: 33093329 No abstract available.

References

    1. Centers for Disease Control and Prevention. Web-based Injury Statistics Query and Reporting System (WISQARS). https://www.cdc.gov/injury/wisqars/index.html. Accessed February 21, 2019.
    1. Gani F, Sakran JV, Canner JK. Emergency department visits for firearm-related injuries in the United States, 2006–14. Health Affair. 2017;36(10):1729–1738. - PubMed
    1. Centers for Disease Control and Prevention. National Vital Statistics System, Mortality 2015. Atlanta, GA: Centers for Disease Control and Prevention; 2017.
    1. Santaella-Tenorio J, Cerdá M, Villaveces A, Galea S. What do we know about the association between firearm legislation and firearm-related injuries? Epidemiol Rev. 2016;38(1):140–57. - PMC - PubMed
    1. Corporation RAND. The Science of Gun Policy: A Critical Synthesis of Research Evidence on the Effects of Gun Policies in the United States. Santa Monica, CA: Rand Corporation; 2018; Retrieved December 31, 2018 from: https://www.rand.org/pubs/research_reports/RR2088.html - PMC - PubMed

Publication types