When he announced his candidacy for president in mid-June, Donald Trump made the provocative assertion that Mexican immigrants are “bringing crime.” The comment gained greater resonance when, two weeks after Trump’s speech, Kathryn Steinle was shot and killed in San Francisco by an illegal alien from Mexico. The alien, Francisco Sanchez, had been in local police custody back in April, and federal officials intended to deport him. But Sanchez was instead released due to San Francisco’s “sanctuary city” policy.
In response to the resulting outcry, some mainstream media outlets correctly noted that, although good data are hard to come by, the overall immigrant crime rate does not appear to be especially high. But then advocates of mass immigration went much further, making wild claims that Mexican immigrants have a miniscule crime rate that somehow even suppresses native crime. Only an uninformed rabble-rouser would worry about criminals crossing our borders, according to immigration enthusiasts.
The truth is more complex. In a detailed report, a colleague and I have explained why it is very difficult to measure immigrant crime. There is research showing that immigrants do commit a disproportionate share of crime, but there is also research showing that the opposite is the case. Census Bureau data collected on the institutional population (such as those in prisons and jails) might be a way to at least measure incarceration rates in an unbiased fashion. But as we explained in the report mentioned above, the Bureau's ability to record whether the institutionalized are immigrant or native broke down in the past and it is still not clear if this problem has been entirely corrected.
There is also the issue of what should be the proper benchmark for measuring immigrant crime. As we point out in our crime study:
In social science research, raw numbers need to be placed into some kind of context, often by comparing one population of interest to another. Assuming one can measure immigrant crime, the next question that arises is: To what should it be compared? This is an important question because crime rates among natives differ widely by group. For example, the share of native-born black men arrested or incarcerated is dramatically higher than for all other groups… However, the discrimination and racism black Americans have experienced and the severe social problems that exist in some black communities make this population unique when it comes to the issue of crime. One can reasonably ask whether it makes sense to compare immigrants, who are overwhelmingly not black, to black Americans who have a unique historical experience.
Data collected by the Census Bureau in 2013 shows that 23 per 1,000 male Mexican immigrants ages 18 to 40 are institutionalized (mainly in jails or prisons; few people at that age are in nursing homes or similar institutions). This compares to 31 per 1,000 for native-born men in this age group. However, looking at only non-black native men (18-40) shows an incarceration rate of 20 per 1,000. This is somewhat lower than the rate of Mexican-born men and a good deal lower than the 38 per 1,000 for U.S.-born men of Mexican ancestry. It is also worth noting that Mexican men are included in the figure for non-black natives; if they are excluded then the rate for natives would be 18 per 1,000. The rate for native-born whites alone is 16 per 1,000.
All this matters because studies that examine what happens to crime rates in predominately black areas when immigrants move in are looking at communities with crime rates that reflect the marginalization and unique situation of black Americans. When it comes to crime, these communities are statistical outliers. So even if crime falls as the immigrants arrive, it is somewhat misleading because the baseline rate was unusually high in the first place. Further, the impact of Mexican immigration on other communities, with much lower pre-existing crime rates, could be very different.
Two other points are worth making with regard to immigrant crime. First, the crime rate of immigrants generally, or illegal immigrants in particular, is irrelevant to the issue of sanctuary cities, which as a matter of policy release illegal immigrants from jails even after Immigration and Customs Enforcement asks them to hold these individuals. That policy is directly responsible for Steinle's death and for the deaths of many others over the years – regardless of statistics about overall crime rates. The public is right to be outraged.
Second, immigration is supposed to benefit our country. Therefore the goal of policy is to select immigrants that have much lower crime rates than natives, not rates that are somewhat higher or even somewhat lower than natives'. Given the strong correlation between crime and educational attainment, moving away from our current system that selects immigrants based primarily on whether they have a relative in the U.S. to one that emphasizes education levels would be one way to move toward such a goal.