Politicians, journalists and immigration experts for years have claimed there are about 11 million illegal aliens in the country, but a new study by three Yale University professors says the actual total is 22 million. Or more.

“Using mathematical modeling on a range of demographic and immigration operations data, the researchers estimate there are 22.1 million undocumented immigrants in the United States,” according to Yale Insights, a publication of the Yale School of Management.

“Even using parameters intentionally aimed at producing an extremely conservative estimate, they found a population of 16.7 million undocumented immigrants,” the publication said of the study, conducted by professors Mohammad Fazel-Zarandi, Jonathan Feinstein, and Edward Kaplan.

Related: Study Details Thousands of Illegal Voters in ‘Sanctuaries’

The study is sparking an uproar among immigration advocates.

A spokesman for the Migration Policy Institute (MPI) told The Washington Times Tuesday: “We believe these new numbers represent at most an interesting academic exercise, but are ultimately greatly off-base and thus counterproductive to the public’s very real need to understand the true scope of illegal immigration and how best to address it.”

The MPI favors liberal immigration policies.

Feinstein, in a video statement on Friday, emphasized the study focuses entirely on data, not on the policies government should follow in dealing with illegal immigration.

“This paper is not oriented towards politics or policy. I want to be very clear. This paper is about coming up with a better estimate of an important number, and we are really trying in this paper to keep away from making any statements about how that could or should be used. It is just a paper to help the debate be organized around some better information, which in my opinion is a good thing to do,” he said.

President Donald Trump was elected in 2016 on a platform promising to “build the wall” at the U.S. border with Mexico, where illegal immigration has surged in recent years. Many U.S. cities and at least one state, California, are self-declared “sanctuaries” for illegal aliens.

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Congress has not yet approved the estimated $25 billion required to build the physical structure everywhere it is possible to build it along the 1,800-mile border.

Trump has vowed to veto funding measures that don’t include the required resources.