Evaluating a national anti-firearm law and estimating the causal effect of guns on crime

We report two results. First, we evaluate the impact of a nationwide anti-firearm legislation passed by the Brazilian Congress in December 2003 (Estatuto do Desarmamento, henceforth ED). Our identification strategy hinges on the hypothesis that the law had stronger impact in places where gun prevalence was higher in the baseline. We find evidence that homicides (reduced form) and firearms prevalence (mechanism or first-stage) dropped faster in places with higher gun prevalence after the 2003. Using our preferred estimates, the ED saved between 2,000 and 2,750 lives from 2004 through 2007 in cities with more than 50,000 inhabitants in the state of São Paulo. Second, assuming the ED causes homicide only through its impact on firearms prevalence, we recover a causal estimate of the impact of firearms on homicides. One standard deviation in the prevalence of firearms reduces homicides by quarter of a standard deviation. We find no impact of both ED and firearms on property crime in general or on robberies. -- homicide ; Brazil ; firearms, gun violence ; property crimes