Ann Coulter’s new book Adios America argues that immigration is undermining the country, and she was delighted to give a full-throated defense of her stance in an interview with Univision and Fusion TV journalist Jorge Ramos. The two agreed on virtually nothing, including the most basic statistics.

Ramos opened the segment of his show America with Jorge Ramos by telling Coulter that her facts on the number of undocumented immigrants were wrong. In her book, she claimed there are 30 million. The consensus figure is about 11 million. Coulter was unfased.

"You’re wrong," Coulter told Ramos. "The number we keep hearing is 11 million, 11 million, 11 million. That’s so weird. It’s been 11 million for a decade. But as I explain in the book, they are all using the Census figures. If the Census figures are wrong, then everybody’s numbers are wrong."

Coulter said there is "absolutely no question" that the number is at least 30 million. She said the work of two Pulitzer Prize-winning journalists and a 2006 analysis by two Bear Stearns financial analysts supported her belief. We’ll touch on those items in a bit.

But arguably Coulter’s biggest numerical claim was that "America has already taken in one-fourth of Mexico's entire population." She said it during her interview with Ramos and included it as a bullet point on her website.

Several readers asked us to dig into that claim. We tried to reach Coulter through her publisher and other channels and did not hear back. However, she gives the source of her figure in her new book.

Coulter’s math

Coulter zeros in on Mexico to undercut the argument that immigration promotes diversity. "Diversity in immigration ought to mean every country on earth sends the same percentage of immigrants," she writes. In contrast, Mexico provides about a third of all immigrants, and that became her target.

In a sub-section titled "Doesn’t Mexico want any Mexicans?" Coulter grounds her statement about America taking in one-quarter of Mexico’s population on a Pew Research Center analysis of census data. The top line number in that study finds that about 33.5 million people of Mexican origin lived in the United States in 2011.

Coulter argues that since Mexico has about 120 million people, and one-quarter of that is 30 million, therefore, America has "taken in" one-quarter of the total.

Misreading the data

In reality, the immigration data from Pew is not nearly as neat and tidy as Coulter concludes. The Pew report attempted to count the number of people who trace their roots back to Mexico, not people who came directly from that country.

Why does that make such a difference?

Well, about two-thirds of Americans with Mexican ancestry were born in the United States. By definition, they were never part of Mexico’s population.

If they weren’t Mexican, they could not be "taken in."

The Pew definition is important, and if the numbers about Mexico don’t make it clear, let’s look at another country. We picked Ireland. In 2014, the Census Bureau said there were 34.1 million Americans with Irish roots. That’s nearly seven times Ireland’s current population.

One could argue that if the parents hadn’t moved to the United States, the children wouldn’t have been born here. But Coulter offers no analysis and no data on that front. In her framework, a person whose family came from Mexico 70 years ago is just as much a Mexican as someone who arrived yesterday.

According to the Census Bureau, about 10.5 million people of Mexican heritage come from families in which both parents were born in the United States. This group is at least second-generation American born.

The Pew report found that about 11.6 million people of the 33.5 million total had been born in Mexico, including both authorized and unauthorized immigrants.

Estimating the undocumented

Tangentially related to this fact-check is Coulter’s suggestion that groups are severely undercounting the number of unauthorized illegal immigrants based on census data.

Coulter’s starting point is a 2005 article from two Bear Stearns financial advisors . They set census data aside and looked at things like the rise in money sent back to Mexico and housing permits in three New Jersey communities with growing immigrant populations. The article said the increases were much larger than the official rise in population. The authors did not show how they reached their estimate of 20 million illegal immigrants, but they, and Coulter, emphasized that "the assumption that illegal people will fill out a census form is the most ridiculous concept I have ever heard of."

The Center for Immigration Studies, a group that favors reduced immigration much as Coulter does, disagrees with that last point.

In a recent report , the center wrote "It is well established that illegal aliens do respond to government surveys such as the decennial census and the Current Population Survey."

"For illegals, we estimate 11 to 12 million with 50 to 60 percent from Mexico," said Steven Camarota, the center’s director of research.

Jennifer Van Hook, who directs the Population Research Institute at Pennsylvania State University, said she believes the number of unauthorized Mexican immigrants living in the United States is 6.3 million-8.3 million. No matter how you slice it, Coulter’s claim doesn’t get any closer to true, she said.

"There is no way it is as high as 30 million," Van Hook said.

The Migration Policy Institute estimates the total unauthorized population at 11 million. Director of research for American programs Randy Capps said figures produced by the Census Bureau’s American Community Survey are just the starting point in determining that figure (the Census Bureau itself doesn't create a count). The final estimate reflects a hike of "20 to 25 percent to address the undercount of unauthorized immigrants in the ACS."

Capps emphasized that his group, the Department of Homeland Security, the Pew Research Center and the Center for Immigration Studies generally reach the same results because they all tweak the census data.

"All four of these sources incorporate an undercount of unauthorized immigrants ranging from 10 to 25 percent," Capps said.

Capp’s counterpart at the Pew Research Center, Jeffrey Passel, rejected Coulter’s claim on both methodological and common sense grounds.

"It is simply not possible for there to be in excess of 30 million Mexican immigrants in the United States," Passel said. "There are not enough houses available in the country for the 20 or so million more additional Mexicans. Moreover, the Mexican censuses, and surveys are completely inconsistent with such figures."

Our ruling

Coulter said that America has taken in one-quarter of the entire population of Mexico. Coulter based this on a study that counted all people of Mexican origin in the United States.

But Coulter ignored that 65 percent of those were born in America and about a third came from families in which both parents were born in America. Their immigrant status lay at least two-generations in the past, and America couldn’t "take them in" because they were already here.

We rate this claim Pants on Fire.

Note: This claim was fact-checked as one of the donor-benefits tied to our Kickstarter campaign to live fact-check the 2015 State of the Union. Thanks to all who contributed.