evidence: Generally accepted estimates put the population of undocumented immigrants in the United States at approximately 11.3 million. A new study, using mathematical modeling on a range of demographic and immigration operations data, suggests that the actual undocumented immigrant population may be more than 22 million. Immigration is the focus of fierce political and policy debate in the United States. Among the most contentious issues is how the country should address undocumented immigrants. Like a tornado that won’t dissipate, arguments have spun around and around for years. At the center lies a fairly stable and largely unquestioned number: 11.3 million undocumented immigrants residing in the U.S. But a paper by three Yale-affiliated researchers suggests all the perceptions and arguments based on that number may have a faulty foundation; the actual population of undocumented immigrants residing in the country is much larger than that, perhaps twice as high, and has been underestimated for decades. 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. Even using parameters intentionally aimed at producing an extremely conservative estimate, they found a population of 16.7 million undocumented immigrants.