evidence: The undocumented population in the United States could be twice as large as the most commonly-used estimate, according to a research study published Friday in the scientific journal Plos One. The paper, led by Mohammad M. Fazel-Zarandi, a researcher at Yale and Massachusetts Institute of Technology, estimates there are 22.1 million undocumented immigrants in the United States. Fazel-Zarandi’s study compared inflows and outflows of immigrants as well as demographic data. According to the report, the number of undocumented immigrants could be as low as 16.5 million, or as high as 29.1 million.