President Donald Trump has claimed that "illegal immigrants pouring into our country [are] bringing with them crime, tremendous amounts of crime." But there is practically no evidence to support such a suggestion, and lots that suggest otherwise.
Restrictionists cite a February study by economist John Lott that used Arizona corrections data to claim that illegal immigrants are more than twice as likely to commit crimes than other state residents. But Lott's findings are highly contested by other researchers. For example, the Cato Institute's Alex Nowrasteh used better-quality data from the Texas Department of Public Safety to report that the "conviction and arrest rates for illegal immigrants were lower than those for native-born Americans."
Now a study in the journal Criminology has examined immigration and crime data from all 50 states from 1990 and 2014. The paper, written by Michael Light of the University of Wisconsin and Ty Miller of Purdue, finds that "undocumented immigration does not increase violence. Rather, the relationship between undocumented immigration and violent crime is generally negative."
"More undocumented immigration meant less violent crime," notes University of Wisconsin press release promoting the study. Indeed, "a 1 percent increase in the proportion of the population that is undocumented is associated with 49 fewer violent crimes per 100,000 people." Why would that be? Light observes that "immigrants are driven by pursuit of education and economic opportunities for themselves or their families. Moreover, migration—especially undocumented migration—requires a lot of motivation and planning. Those are characteristics that aren't highly correlated with a high crime-prone disposition."