Association for Public Policy Analysis & Management

Over the past thirty years, crime rates in cities across the United States have plummeted, in many cases, reaching fifty-year lows. At the same time, the share of the foreign born among the U.S. population has increased rapidly, with the foreign-born Mexican share of the population quadrupling since 1980. Though most recent empirical work is consistent with patterns in the aggregate time series, the available literature rarely disaggregates the effects of immigration on crime by nationality. In particular, there is little research that addresses the criminal participation of recent and specifically undocumented Mexican immigrants which is precisely the population that has become the focal point of recent policy debates.

Because it is difficult to identify exogenous variation in undocumented immigrant flows and because IV estimates are difficult to interpret as policy relevant quantities, there is promise in searching for a natural experiment — in particular, one that is rooted in a realistic policy option for manipulating the stock of undocumented immigrants in the United States. In the spirit of Card’s seminal 1990 research on the labor market impacts of the Mariel Boatlift on Miami, we leverage a remarkable natural experiment created by recent legislation in Arizona to estimate the impact of an extremely large and discrete decline in the state’s foreign-born non-citizen Mexican population. We show that Arizona’s non-citizen Mexican population decreased by as much as 20 percent in the wake of the state’s 2008 implementation of the Legal Arizona Workers Act (LAWA), a broad-based “E-Verify” law coupled with severe sanctions for noncompliance (Bohn, Lofstrom and Raphael 2013). By contrast, the law appears to have had no effect on the state’s share of other non-citizens or U.S.- born Hispanics. In order to isolate the causal effect of the passage and implementation of LAWA on crime, we employ a synthetic “differences-in-differences” estimator, a method of counterfactual estimation for case studies proposed by Abadie, Diamond and Hainmuller (2010). To calculate a direct estimate of the effect of Arizona’s Mexican immigrant share on its crime rate, we extend the synthetic differences-in-differences framework to construct implied synthetic instrumental variables estimates, using LAWA as an instrument for the Mexican population share.

In contrast to previous literature, we find some evidence in favor of a contribution of Mexican immigration to property crime in Arizona. The estimates are robust to a variety of specification checks including changing the composition of the synthetic comparison group as well as using agency-level and monthly data and are supported by a series of placebo tests that examine the impact of dummy E-Verify laws in states that never received one. However, results are driven, in large part, by the fact that LAWA resulted in especially disproportionate declines among Mexican migrants who are young and male and, as such, the effects are entirely compositional. Indeed, for most crimes, the treatment effect is fully explained by age and gender composition and, consistent with prior literature, the results suggest that young Mexican men are less likely to engage in crime than young native men.