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Controversial new study purports to show that illegal immigrants commit more crime. But do they?

Existing data can make it difficult to tell just how often illegal immigrants end up in prison

Scott Eisen/Getty Images

Are illegal immigrants more likely or less likely than American citizens to commit crimes? The answer to this question could have a tremendous impact on the ongoing immigration debate in our country.

Within the last year, two studies were published on the rate of incarceration for illegal immigrants with vastly differing results. One said that illegal immigrants committed crimes at about half the rate of American citizens, another said that they were three times more likely.

Both results match the biases of the authors, both sets of authors have objections to the data and methodology used by the other, and both dismissed criticisms leveled at their own analysis during interviews with TheBlaze.

Can they both be right?

A large part of the problem that led to this discrepancy stems from the fact that there is no one set of government data that shows the exact number of illegal immigrants who are incarcerated in each state for an entire given year. So researchers have to come up with creative ways to deduce that information by looking at other factors. These methods can lead to widely different results.

What do these studies say?

At the outset, it should be noted that neither study purports to show how often illegal immigrants actually commit crimes, but rather how often immigrants are CAUGHT committing crimes, based on how often they are incarcerated. It should go without saying that many illegal immigrants commit a crime by crossing the border illegally to get to the United States.

Yes, the proper way to describe that number is "many," not "all." Crossing the border illegally is a misdemeanor crime, but the majority of current illegal immigration happens through visa overstays, which is a civil (non-criminal) offense.

Neither study was able to isolate incarcerations that were solely for illegal border crossings and examine the thorny question of how much crime illegal immigrants commit once they have arrived in the United States, whether through an illegal border crossing or through a visa overstay.

However, both studies used what data exists to attempt to prove two very different conclusions.

On Feb. 3, the Federation for American Immigration Reform (FAIR), a group in favor of restricting illegal immigration, put out a study claiming that illegal immigrants are on average three times more likely than American citizens to be incarcerated.

In June, the CATO Institute, a libertarian think tank that takes a more favorable view of immigration, ran a study claiming that illegal immigrants were only about half as likely to be incarcerated as their native-born counterparts.

Both studies cited U.S. government data from 2016, but their conclusions are mutually exclusive.

The danger in studies with results that are this different is that politicians, pundits, and activists can take whichever study they feels most supports their point of view.

The data sources are different

The most important difference between the two studies is the source material. The FAIR study relies on data from the State Criminal Alien Assistance Program (SCAAP). According to the Department of Justice, SCAAP "provides federal payments to states and localities that incurred correctional officer salary costs for incarcerating undocumented criminal aliens with at least one felony or two misdemeanor convictions for violations of state or local law, and incarcerated for at least 4 consecutive days during the reporting period."

FAIR only looked at the 10 states with the densest populations of illegal immigrants. These states include 65 percent of the illegal immigrant population (according to FAIR), but only about 43 percent of the total U.S. population (according to the U.S. Census Bureau).

The CATO study relies instead on American Community Survey data from the U.S. Census Bureau. Rather than rely on illegal immigrants to self-report their status, the authors of the CATO study looked at factors that might indicate that a person was an illegal immigrant. For example, illegal immigrants likely wouldn't be in the military, and cannot receive Social Security or Railroad Retirement Income.

The CATO study also includes federal arrests, including by Immigration and Customs Enforcement, while the FAIR study only looks at arrests on a state and local level. CATO argued that, if anything, its methods for identifying illegal immigrants might inadvertently include legal immigrants who had been incarcerated, and that the number could be even lower.

Alex Nowrasteh, one of the authors of the CATO study, told TheBlaze that its final result was "almost certainly an over-count" and that CATO's "estimates of the illegal immigrant incarcerated population and incarceration rate are likely greater than the actual population and rate." However, there is no way to know this.

The two groups also used different numbers for the total estimate of all illegal immigrants living in the United States in 2016. CATO cited that number as 14.7 million, while FAIR cited it as 12.5 million. A larger total illegal immigrant population would mean that the same number of incarcerated illegal immigrants would represent a smaller percentage, and vice versa. This would skew the numbers slightly in favor of each author's bias, but not enough to account for the total discrepancy.

FAIR's reliance on SCAAP data also opens itself up to a margin of error from illegal immigrants who entered the system twice in one year. Any time an illegal immigrant is in the prison system for more than four days, the state or local prison can bill the federal government. The total number from SCAAP isn't a number of individual prisoners, but a number of reimbursements for specific incidences of holding prisoners.

It's also possible for multiple state and local prisons to transfer an illegal immigrant prisoner and all bill the federal government through SCAAP for holding the same person. In these cases, the SCAAP numbers would make it look like two or more people had been incarcerated instead of just one.

FAIR admitted that this was possible, but said that it would only happen in "very rare situations." FAIR pointed out to TheBlaze that, on average, prisoners in the SCAAP system spent 6 1/2 months in custody for a single request."

However, since this is an average, it's impossible to tell how much of a difference this could make.

TheBlaze asked one of the authors of the FAIR study about the possibility of state and local prisons filing fraudulent SCAAP reports. FAIR also dismissed this as being unlikely. And they could be right.

Study co-author Spencer Raley told TheBlaze that "SCAAP sets the rules for reimbursement, and they only cover a small portion of the total costs. So states/counties can't really make extra money by over billing." But without a prison by prison review of all SCAAP records, this is impossible to verify.

Finding out the real number could be impossible

The different conclusions reveal a deeper problem with studies like this: without a direct number from the government, researchers have to arrive at the data in creative ways.

But even if there was an official government-produced number for how many illegal immigrants are in prison at any one time, there would still be questions as to its accuracy. State and local governments don't always accurately report figures like this to the federal government. The disparity in the results between these two studies show just how different the reporting data can be. The census number for how many illegal immigrants are in prison should match exactly with the number of reimbursements collected by state and local prisons. But it doesn't.

Until such a time, if ever, that better data becomes available, readers should take all such studies with a grain of salt and take into account the biases of the group producing the study.

One last thing…
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