Does the Stand Your Ground law reduce murder?

The Stand Your Ground (SYG) law gives individuals the ability to defend themselves with deadly force without the duty to retreat, if they have reasonable belief that they are in danger of great bodily harm or death. It has been passed in 30 states in the U.S. However, researchers have examined crime data and mortality data to show that the SYG law causes an increase in murder rate compared with states that do not have the law. A new study shows that the increase differs between planned murder and unplanned murder.

The study uses game theoretical models to show that there is an arms race" between planned murder offenders and victims and an "escalation of violence" between unplanned murder offenders and victims after the SYG laws. In response to victims' increase in self-defense preparations, planned murder offenders increase their level of preparation, resulting in an "arms race." In response to victims' increased self-defense efforts, unplanned murder offenders increase their criminal efforts, thus "escalation of violence."

Data analysis confirms the model predictions. Compared to states with no SYG laws, states with them have an approximately 8% increase in planned murder and approximately 10% increase in unplanned murder. Researchers attribute the increase of planned murder to the increase in murder success rate and the increase in unplanned murder to the fact that less serious crimes have turned into murder.

Based on these results, researchers encourage states that have not passed the law to vote down on proposals for it and states that have passed the law to repeal it.