We will be addressing this matter multiple times as we explore in the future alternative ways of measuring the size of this population. This posting focuses on methods of measurement.
The Center for Immigration Studies summarizes how the Federal Current Population Survey handles this matter, in its Immigrants at Mid-Decade: A Snapshot of America’s Foreign-Born Population in 2005.
It is well established that illegal aliens do respond to government surveys such as the decennial census and the Current Population Survey. While the CPS does not ask the foreign-born if they are legal residents of the United States, the Urban Institute, the former INS, the Pew Hispanic Center, and the Census Bureau have all used socio-demographic characteristics in the data to estimate the size of the illegal population.15 Our preliminary estimates for the March 2005 CPS indicate that there were between 9.6 and 9.8 million illegal aliens in the survey. It must be remembered that this estimate only includes illegal aliens captured by the March CPS, not those missed by the survey. By design this estimate is consistent with those prepared by the Census Bureau, Immigration and Nationalization Service (INS), Urban Institute, and Pew Hispanic Center.16 While consistent with other research findings, it should be obvious that there is no definitive means of determining whether a respondent in the survey is an illegal alien with 100 percent certainty. We estimate that in 2000, based on the March 2000 CPS, that there were between seven and 7.2 million illegal aliens in the survey. This means about 2.5 to 2.7 million, or about half of the 5.2 million growth in the foreign born between 2000 and 2005 was due to growth in the illegal population. We also estimate that 3.6 to 3.8 million or almost half of the 7.9 million new arrivals are illegal immigrants.