Nearly 3 percent of illegal immigrants in Arizona end up in state prison or jail during the course of a year — four times the rate of U.S. citizens and legal residents, according to a study that uses federal reimbursements for prisons and jails to try to calculate one of the most important yet elusive statistics in the immigration debate.
In New Jersey, illegal immigrants are incarcerated five times more often, and rates on the West Coast are triple that of legal residents and citizens, according to the study by the Federation for American Immigration Reform.
FAIR based its calculations on federal government reimbursements to states and localities under the State Criminal Alien Assistance Program, which pays some of the costs for holding illegal immigrants in prisons and jails. To make the payments, the federal government must determine whether an inmate is definitely or possibly in the country illegally. FAIR used the number to then calculate overall incarceration rates.
The method is not without controversy. One analyst dismissed the calculations, saying SCAAP data counts are not comparable to other incarceration counts.
But FAIR says the SCAAP numbers are the best calculation because they focus on those known to be arrested on criminal charges and whom federal officials have concluded are in the country illegally.
In the 10 states FAIR selected, they determined that illegal immigrants ended up behind bars at higher rates, per capita.
“This study should put to rest, once and for all, the notion that illegal aliens commit crimes at a lower rate than legal residents,” FAIR President Dan Stein said. “By focusing on states with significant illegal alien populations and that consistently report to the SCAAP program, FAIR’s study refutes this erroneous claim.”
Illegal immigration and its nexus to crime, long a controversial subject, has gained even more importance in recent weeks as President Trump has pushed for stiffer border security — including a border wall — that he says would “bring crime down in half in our country.”
FAIR, which advocates for a crackdown on illegal immigration, doesn’t quite answer that question, but it does attempt to get at the overall rates of criminal behavior of people whom the government has confirmed are in the country illegally, and then to compare that to the rate of criminality by the rest of the population.
The group took a snapshot of the prison population in a state, using data from the Prison Policy Initiative, then subtracted the number of illegal immigrants the federal government paid to incarcerate in a year. That provided numbers for both an illegal immigrant prison population and everyone else.
FAIR then compared those with estimates for the overall residential numbers for each state.
For Arizona, analysts used 10,300 confirmed or suspected illegal immigrants for which the federal government reimbursed the state and counties in 2016. They subtracted that from an overall prison and jail population to get a non-illegal-immigrant population of 46,700.
Each of those numbers was stacked up against total populations. FAIR estimates that Arizona has an illegal immigrant population of 365,950 and non-illegal-immigrant population of 6.7 million. Incarceration rates were 2.815 percent for illegal immigrants and 0.702 percent for all others.
That means one out of every 35 illegal immigrants in Arizona was in state prison or jail in 2016, which was the highest rate of any of the states they studied.
They did the same calculations for nine other states that have strong SCAAP reporting and account for about three-quarters of the estimated illegal immigrant population in the country.
In each of the 10 states, they found illegal immigrants incarcerated at higher rates. The gap was biggest in New Jersey, with an illegal immigration jail rate 440 percent higher, followed by Arizona, Oregon, Washington and California in the top five.
New York and Nevada came next, with rates at least 160 percent higher, followed by Florida, Texas and New Mexico, with the smallest gap — though even there, illegal immigrants were 42 percent more likely to be in prison or jail than the citizen and legal resident population.
John R. Lott Jr., president of the Crime Prevention Research Center, said FAIR’s research gets around two issues that plague a lot of other research on illegal immigrant crime rates.
Many studies rely on survey data, such as the census, to ask about criminal pasts. But Mr. Lott said that if people are reluctant to take part in the census because they fear answering citizenship questions, then they might refuse to take part or might shade their answers if they are illegal immigrants with criminal records. He said that would skew the results of crime rate studies based on census data.
Another type of study looks at all immigrants combined, without dividing out legal residents and illegal immigrants.
Mr. Lott’s research, using data from Arizona that differentiates between immigrants, found that legal immigrants had the lowest rates of incarceration, with citizens in the middle and illegal immigrants with the highest rates of crime.
“FAIR here has stuff from multiple states indicating that if in fact they’re right on all this, it’s pretty much systematically true across all prison systems and jail systems,” he said.
But Alex Nowrasteh, a senior immigration policy analyst at the Cato Institute, questioned FAIR’s methodology. He said the data used to calculate the overall prison population doesn’t link up with the SCAAP data, so trying to make incarceration comparisons doesn’t work.
“The way that the government measures the number of SCAAP prisoners is different than the way they measure any other type of prisoners in the United States,” he said. “I’d need to measure other prison populations in the same way the government measures SCAAP prisoners because the SCAAP is a combination of both the number of prisoners in prison and the number admitted over a period of time.”
Mr. Nowrasteh conducted such a calculation for SCAAP numbers nationally, for data from 2006 to 2015. He found that as a percentage of their respective subpopulations, illegal immigrants are less likely to be incarcerated nationwide than native-born Americans and legal residents.’
In 2015, for example, he found the incarceration rate of illegal immigrants at 486.8 per 100,000, versus 673 per 100,000 for citizens and legal residents.
The SCAAP data that FAIR used doesn’t delve into the specific crimes covered, so it’s impossible to say from the data whether one population tended toward more serious offenses compared with the other.
Other potential problems with the SCAAP data include the risk of double-counting because the numbers give only an aggregate of inmate stays. If someone is in a local jail and then a state prison for the same offense in the same year, then they could be double-counted.
FAIR, though, says the conditions of SCAAP money — someone must have a felony or two misdemeanor convictions — plus the average length of stay means the rate of double-counting is likely small.
Other studies have tried to get at the illegal immigration crime question other ways.
A study published last March in the journal Criminology found that communities with higher levels of illegal immigrant populations had lower levels of crime. Michael T. Light, a sociologist at the University of Wisconsin-Madison, calculated that a 1 percent increase in the unauthorized population meant 49 fewer crimes per 100,000 people — the typical yardstick for crime rates.
Given that, they concluded, immigration enforcement may backfire by raising crime rates beyond what they otherwise would be.
Mr. Nowrasteh, meanwhile, has conducted his own work based on criminal conviction and arrest data in Texas. He found that as a percentage of the population, illegal immigrants amassed 50 percent fewer convictions than native-born Americans, and legal immigrants rated even lower.
Among homicides in particular, of 785 convictions in Texas in 2015, 709 were native-born, legal immigrants were 30 and illegal immigrants were 46. That works out to rates of 3.1 per 100,000 for native-born, 1 per 100,000 legal immigrants and 2.6 per 100,000 illegal immigrants.