Researchers at the Yale School of Management have estimated the number of undocumented immigrants in the United States to be nearly twice as large as the number widely accepted and extrapolated from the Census Bureau’s annual American Community Survey.

The study, conducted by Yale professors Jonathan Feinstein and Edward Kaplan as well as MIT lecturer Mohammad Fazel-Zarandi, used demographic modeling data to produce a range of 16.2 million to 29.5 million undocumented immigrants in the U.S., with an average estimate of 22.1 million. The study was published on Sept. 21 in the journal PLOS One.

This number — 22.1 million — stands in contrast to the widely accepted estimate of 11.3 million, a number frequently referenced by politicians in recent elections.

Being an immigrant himself, Fazel-Zarandi knows how important the number of undocumented immigrants is to public policy and discourse in the U.S. Thus, he was inspired to start this research under the guidance of Kaplan and Feinstein.

“A lot of people said ‘don’t do it, it’s a problem they’ve been working on for 30 years’ … When I saw they were using surveys, I knew there must be something wrong,” Fazel-Zarandi said.

Kaplan said the researchers began the study to check the validity of the currently estimated number but instead found a number that exceeded current estimates, even when conservative constraints were applied. The earlier method used census-generated population estimates, Kaplan explained, which can underestimate populations by up to 10 percent.

“The single most important thing is that although we’re coming up with a much larger number, it’s not something that has happened all of a sudden,” Kaplan said. “It’s not that we have zillions of people pouring across the border. If you actually look at the figures, you’ll see that the number has actually been flat for the last 10 years.”

To estimate change in the undocumented immigrant population, the study used demographic data in conjunction with information such as the number of deportations and visa overstays reported by law enforcement agencies. Modeling the population size using a simulator, the researchers found the number of individuals to be 16 to 29 million people.

The researchers began by producing a “conservative estimate,” meaning they deliberately tried to make their estimate as small as possible, Kaplan explained. The researchers did this by plugging into their data the lowest possible rate of undocumented immigrants entering the country and the highest possible rate exiting. This produced an estimate of 16.7 million — still nearly 50 percent higher than the previous figure of 11.3 million.

Kaplan noted that statistics such as per capita crime rate and job displacement due to undocumented immigration significantly drop in light of the different population size estimate.

“What our results say is we have the same number of crimes, but we’ve spread it to twice as many people,” Fazel-Zarandi said. “This means the per capita rate is half as big.”

Additionally, many undocumented immigrants depend on nonprofits for services such as emergency healthcare and legal services. This study suggests that nonprofits may actually have many more immigrants to cover than previously thought, Fazel-Zarandi explained.

Feinstein emphasized that policymakers should recognize the large degree of uncertainty in estimating the size of a hidden population. He added that researchers in the field experience some political obstacles to their work, which can prevent effective constructive criticism.

“The main challenge has been with politically-motivated individuals who have made it difficult to have an open discussion and even a smooth publication process around the work,” Feinstein said.

The study also had broader implications, in both other areas of public life and among different hidden populations. This type of mathematical modeling has actually been used for years, Fazel-Zarandi said, to study numbers of drug users, tax evaders, homeless people and other groups that wouldn’t necessarily want to respond to surveys.

“It’s hard to find these populations,” he said, “and even if we find them, they may have an incentive to lie.”

Other undocumented immigration research centers, however, have pushed back against the 22 million statistic.

The Migration Policy Institute and Center for Immigration Studies released statements and papers disagreeing with the new findings, while the Pew Research Center has decided to stick with their number of 11 million undocumented immigrants.

In 2016, 753,060 people became naturalized U.S. citizens, according to CNN.

Asha Prihar | asha.prihar@yale.edu

Josh Purtell | josh.purtell@yale.edu

Emmett Shell | emmett.shell@yale.edu