How we guess number of undocumented immigrants

Today’s question: Recently a story in the paper said, “Undocumented immigrants remain steady at 11.1 million.” If they are undocumented, how do we know how many there are? This one is so easy it is far too complicated to explain well in this limited space.

In a nutshell, they count up all the immigrants in the country and subtract those who are here legally, such as green-card holders.

Whatever is left is the number of undocumented immigrants. This is known as the residual method.

Of course it is not even close to being that simple.

The leading experts on this seem to be at the nonpartisan Pew Research Center, where they spend a lot of time thinking. Unfortunately for me, they spend a lot of time thinking about numbers, which we all know is something I don’t do.

Those Pew experts rely on data from the U.S. Census Bureau, especially that bureau’s Current Population Survey and the American Community Survey.

Both ask people where they were born and if they are citizens – but not if they are here legally.

They also figure in the usual undercount numbers, demographics such as births and deaths, departures, border apprehensions and so on and so forth. They even take into account census data from Mexico and whatever data they can gain from some Central American countries.

If you want a detailed explanation of this go to pewresearch.org. It might make your brain hurt. But it comes down to a guess – a highly educated and fairly accurate guess, but a guess nonetheless.