Evaluating the impact of Florida’s “Stand Your Ground” self-defense law on homicide and homicide by firearm: an interrupted time series study

Journal article

Importance
In 2005 Florida amended its self-defense laws to provide legal immunity to individuals using lethal force in self-defense. The enactment of “Stand Your Ground” laws in the United States has been controversial and their effect on rates of homicide and homicide by firearm is uncertain.

Objective
To estimate the impact of Florida’s Stand Your Ground law on rates of homicide and homicide by firearm

Design, Setting and Participants
Using an interrupted time series design we analysed monthly rates of homicide and homicide by firearm in Florida between 1999 and 2014. Data were collected from the Wide-ranging Online Data for Epidemiologic Research (WONDER) web portal at the Centers for Disease Control and Prevention. We used seasonally adjusted segmented Poisson regression models were used to assess whether the onset of the law was associated with changes in the underlying trends for homicide and homicide by firearm in Florida. We also assessed the association using comparison states without Stand Your Ground laws (New York, New Jersey, Ohio, Virginia) and control outcomes (all suicides and suicides by firearm in Florida).

Intervention
October 1 2005, the effective date of the law, was used to define homicides “before’ and “after” the change.

Main Outcome Measures
Monthly rates of homicide and firearm related homicide (ICD-10, X85 to Y09; X93-X95).

Results
Prior to the Stand Your Ground Law, the mean monthly homicide rate in Florida was 0.49 deaths per 100,000 with an underlying trend of 0.1% decrease per month. After the law took effect, we found an abrupt and sustained increase in monthly homicide rates of 24.4% (RR 1.24; 95% CI: 1.16–1.33, P=<0.001) and rates of homicide by firearm of 31.6% (RR 1.36; 95% CI: 1.21–1.44, P=<0.001). No evidence of change was found in the analyses of comparison states and of suicides and suicides by firearm in Florida.

Conclusions and Relevance
The removal of a “duty to retreat” under Florida’s Stand Your Ground law was associated with a significant increase in homicides and homicides by firearm.

Authors: Humphreys, D; Gasparrini, A; Wiebe, D

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: American Medical Association
• Journal: JAMA Internal Medicine
• Volume: 177
• Issue: 1
• Pages: 44-50
• Publication date: 2016-11-14
• Acceptance date: 2016-09-16
• DOI: 10.1001/jamainternmed.2016.6811
• EISSN: 2168-6114
• ISSN: 2168-6106
• Keywords: Article