Illegal Aliens 101: How Many Illegals Are There?
By George Borjas
I've received a number of emails asking me to provide some basic information about immigration in the United States. It's a great idea and I'm happy to satisfy the demand.
So let me start with a central issue in the current debate: How many illegal immigrants are there? In recent days, I've seen numbers ranging from 6 to 20 million being floated around--depending on the spin that is being emphasized in any given article.
The basic approach used to calculate this number was first formulated by Jeffrey Passel and Robert Warren (who was then, if I recall correctly, the chief statistician at the INS) and was published in Demography in 1987.
The idea is this: The U.S. Census Bureau regularly surveys the population (as with the decennial Census), and these surveys provide a count of how many foreign-born people live in the country. This count will include many illegals as they try very hard to count people "living in the shadows."
At the same time, the immigration bureaucracy keeps good records on how many permanent residence visas they've granted (i.e., how many "green cards" have been given out). By making a few assumptions about the mortality rate of immigrants, about the number of foreign students in the country, etc., we can predict how many foreign-born people should be living permanently in the country.
The number of illegal immigrants is given by the difference between the Census count of foreign-born persons and the number of foreign-born persons who should be in the United States.
The Department of Homeland Security's website contains reports that summarize the results of this exercise for 2000 and 2005. And this is what the official counts say: The 2000 report estimates 7 million illegal immigrants as of January 2000. The 2005 report estimates 10.5 million illegals as of January 2005. Further, the 2005 report claims that the number of illegals was growing at the rate of 400,000 annually. So if this rate of growth has been roughly the same over the past couple of years, we are nearing the 12 million mark.
Are these numbers credible? Yes....but. There's one underlying assumption in the calculation that, I think, probably leads to an underestimate of the number of illegals. No matter how hard the Census Bureau tries, it cannot possibly count every illegal immigrant in the country. There are some shadows that are way too dark even for the Census Bureau to penetrate. So one has to make an assumption about the rate of undercount of illegals. Before I tell you what they assumed, let me ask you to just think about it for a moment: what fraction of illegals do you think are missed by the Census?
The DHS assumption is that the rate of undercount is 10 percent (see point f on page 2 of the 2005 report). Maybe it's just me, but I think that assumption is on the low side. Given that, my hunch (and it's only a hunch as I have no idea about what the true rate of undercount is) would be that the "true" number of illegal immigrants in the United States right now could easily be 13 to 14 million.
(An interesting aside: For reasons unknown to me--although conspiracy theorists could have a field day--the count of the number of illegal immigrants in 2000, as reported by the contemporaneous 2000 report, is 7 million. But the number of illegal immigrants in 2000 as reported by the after-the-fact 2005 report, is 8.5 million, making it seem as if fewer illegals entered during the Bush years). |
