The United States has belatedly awakened to the knowledge that it is, in effect, under armed attack. More than 30 000 people are purposely shot to death each year—more than 300 000 since the World Trade Center was destroyed in 2001. Rates of firearm-related violent crime have increased 26% since 2008. Physicians have joined others in demanding a strong response to this crisis. We look to scientific research to provide the evidence on which that response should be based. Such evidence should include a thorough exploration of risk and protective factors and, most importantly, controlled studies showing which interventions work to reduce firearm violence and why.

At a time when guidance is urgently needed, Fleegler and colleagues have examined the relationship between firearm laws and firearm-related deaths in the United States. Their state-level ecological study (a design in which the unit of analysis is a population in aggregate, not the individuals in it) correlated the presence or absence of 28 laws arguably related to firearm violence with firearm-related mortality rates. Their main finding is that having more laws on the books is associated with having lower rates of firearm-related homicide and suicide. This would be an important finding—if it were robust and if its meaning were clear.