A recent paper published in the journal PLoS ONE claims that the number of illegal immigrants currently residing in the United States is at least 50 percent greater than previously thought and likely to be twice as high. Researchers Mohammad M. Fazel-Zarandi, Jonathan S. Feinstein, and Edward H. Kaplan write that:
Our conservative estimate is 16.7 million for 2016, nearly fifty percent higher than the most prominent current estimate of 11.3 million, which is based on survey data and thus different sources and methods. The mean estimate based on our simulation analysis is 22.1 million, essentially double the current widely accepted estimate.
That PLos ONE paper levels a serious charge as virtually all demographers and researchers in think-tanks on both sides of the immigration issue and the government think that the real number of illegal immigrants lies somewhere between 11 and 12 million.
Understandably, much of the media has run with this headline finding but have neglected to cite the substantive and convincing criticism published in PLoS One in the same issue. There are three major criticisms of the paper by Fazel-Zarandi, Feinstein, and Kaplan. The first is that their model is highly sensitive to assumptions about return migration in the 1990s. Merely replacing the authors’ assumptions with those based on Mexican return-migrant survey data brings their estimates down to the commonly accepted level. The second is that it is very difficult for millions of additional people to hide in the United States without leaving a demographic or statistical trail. Their children should show up in birth and school records, their deaths should show up in death records, and more of them should be counted in the American Community Survey or U.S. Census. The third is that they should show up in economic surveys of employment, but they do not.
Researchers, pundits, policy-makers, and members of the media should not support the PLoS ONE findings based on the quality of the criticisms. Although my doubts line up well with those of the critics cited above, there are some interesting implications if (a very big nearly-impossible if) the results of the PLoS ONE paper turn out to accurately estimate a greater number of illegal immigrants.