A single change in Florida's gun laws was followed by a 24 percent increase in homicides, a new study has found. Meanwhile, other states saw a decline in gun deaths, increasing the probability that legislation, rather than social trends, led to the extra killings.
From 1999 to 2005, Florida averaged 82 homicides (murders, cases of manslaughter, and killing in self-defense) per month, and the rate appeared to be falling by 0.1 percent a month. Of these, 49 were associated with firearms. In 2005, “Stand Your Ground” legislation came into force and subsequently became notorious when it was used as a defense for the killing of Trayvon Martin. The legislation expanded the circumstances in which people could claim to have used lethal force in self-defense.
A paper in JAMA Internal Medicine reports that from 2005 to 2014, Florida homicides increased by almost a quarter. Moreover, the increase where firearms were involved was 32 percent.
As scientists never cease to remind the public, correlation is not causation, so the authors investigated whether forces other than a poorly timed act of state congress could have caused the additional deaths.
First, the authors looked to see if homicides (with or without guns) were rising elsewhere in the US, which would suggest Florida was simply caught up in the tide. However, New York, New Jersey, Ohio, and Virginia, the four states without similar legislation using consistent monthly reporting of homicide figures, saw major reductions over the same period (as did the country as a whole).
They also tested whether the Global Financial Crisis played a part in the rise, but considered this unlikely after finding that other social problems, historically more closely tied to economic conditions than homicides, did not rise significantly over the same period.
“Given Florida was the first state to extend the use of lethal force in this way, it is an important test case that many other states have since followed,” said lead author Dr David Humphreys of the University of Oxford in a statement. “We hope these findings will inform the ongoing debates about the implications that Stand Your Ground laws may have for public safety in Florida and other US states.”
Co-author Dr Antonio Gasparrini of the London School of Hygiene and Tropical Medicine noted: “Stand Your Ground laws have been implemented across US states since 2005. Surprisingly, in spite of controversy surrounding guns and gun law in the US, very little research analyzing its introduction has been conducted.”
This may be related to a ban on federal funding for most research on gun deaths, which may be why the lead authors came from outside the US.
The same edition of JAMA Internal medicine included a review of 34 papers investigating the effects of five different types of gun laws. The authors concluded that laws making it more difficult to purchase firearms without a permit were associated with reduced homicides, but bans on specific sorts of weapons or the carrying of guns in public places produced either no detectable benefit or unclear results.
Although the prospects for evidence-based reform on this topic might seem slim at the moment, four states held ballots on tightening gun laws, coinciding with the presidential election. Three of these passed, increasing the chance that voters in other states will need to consider similar questions in the future and may benefit from scientific research on the topic.