Many immigration advocates argue that immigrants have much lower crime rates than natives (see this op-ed and this paper). As my colleague Jessica Vaughan and I pointed in a paper some years ago, however, the picture is far from clear. While there are other issues, the biggest problem with studying immigrant crime is that states and localities do not systematically track the country of birth, citizenship, or legal status of those they arrest, convict, or incarcerate. But the federal government does track the citizenship of those it convicts. New data from the U.S. Sentencing Commission shows that of those convicted of federal crimes between 2011 and 2016, 44.2 percent were not U.S. citizens — 21.4 percent, if immigration crimes are excluded. In comparison, non-citizens are 8.4 percent of the adult population. Of this 8.4 percent, about 4 percent are illegal immigrants and about 4 percent are legal immigrants.

The commission's data does not distinguish legal status among non-citizens. It is almost certain that a majority of the non-citizens convicted of federal crimes are illegal immigrants. But we cannot say for sure because that information is not provided. What we can say, at least at the federal level, is that non-citizens are more likely to commit crimes than citizens.

A Very Important Caveat about These Numbers. Those convicted at the federal level are not necessarily representative of all criminal convictions in the United States. Most law enforcement occurs at the state and local level and it is not reasonable to simply extrapolate about immigrant criminality generally from the federal data. Nonetheless, federal law enforcement is still enormous, with 312,000 people (67,000 non-citizens) sentenced in the federal courts between 2011 and 2016, excluding immigration violations. And in the federal system, where we do have good data, non-citizens account for a disproportionate share of those who are sentenced for many different types of non-immigration crimes.

One Additional Caveat. Because it is easier to make an immigration case, federal prosecutors sometimes charge illegal immigrants only with immigration violations, even when they have committed serious non-immigration crimes. Once convicted, an immigrant will still normally serve some time and then be deported, which is often seen by prosecutors as good enough. This, of course, does not happen with citizens. But because of this, conviction data for non-immigration crimes will tend to understate the level of criminal activity among non-citizens.

Among the findings of the new data:

Areas where non-citizens account for a much larger share of convictions than their 8.4 percent share of the adult population include:

42.4 percent of kidnapping convictions;

31.5 percent of drug convictions;

22.9 percent of money laundering convictions;

13.4 percent of administration of justice offenses (e.g. witness tampering, obstruction, and contempt);

17.8 percent of economic crimes (e.g. larceny, embezzlement, and fraud);

13 percent of other convictions (e.g. bribery, civil rights, environmental, and prison offenses); and

12.8 percent of auto thefts.

Areas where non-citizens account for a share of convictions roughly equal to their share of the adult population include:

9.6 percent of assaults;

8.9 percent of homicides; and

7.5 percent of firearm crimes.

Areas where non-citizens account for a share of convictions lower than their share of the adult population include:

4.1 percent of sex crimes;

3.3 percent of robberies;

4.5 percent of arsons; and

0 percent of burglaries.

Data. These tables showing convictions were compiled by the Government Accountability Office at the request of the Senate Judicatory Committee based on data from the U.S. Sentencing Commission "Interactive Sourcebook of Federal Sentencing Statistics". Convictions are in the federal courts for felonies and class A misdemeanors. Death penalty cases and petty offenses are not included. The non-citizen share of the overall adult population comes from the public-use data file of the 2011-2016 American Community Survey collected by the U.S. Census Bureau.