How the Tally of Illegal Immigrants Adds Up, and Why It Matters

*I’ve often wondered how the official estimate of 11 million undocumented immigrants in the U.S. is calculated. Some unofficial tallys put the count at 13 million. There’s no way to know; how do you accurately count people who don’t want to be noticed? So if 11 million, more or less, is the official number, it makes sense to know how the number is calculated. It affects policy, debate and politics. And it turns pout that what’s official is at best a calcualtd guess – is it the best  we can do under the circumstances? VL

By Jo Craven McGinty, The Wall Street Journal

Techniques for calculating the number of illegal immigrants have been around for at least 30 years. Traditionally, the calculation involves something called residual methodology—or, as most of us would think of it: subtraction.

“The process is both simple and complicated,” said Jeffrey S. Passel, a demographer at the Pew Research Center who previously worked for the U.S. Census Bureau. “We determine how many immigrants are in the country legally, and we subtract that from how many are in the country total.”

Until the 1980s, conventional wisdom held that illegal immigrants weren’t represented in government population surveys. But a supplement to the Current Population Survey in the early 1980s asked residents why they didn’t vote, and the number who responded by saying they weren’t citizens exceeded the estimated number of legal immigrants in the same area.

“We discovered nonauthorized immigrants are in the data,” said Robert Warren, a visiting fellow at the Center for Migration Studies who previously was also a demographer at the Census Bureau. “That changed things.”

Using the residual technique, which Messrs. Warren and Passel pioneered, researchers assume all foreign-born residents who entered the U.S. before 1980 or 1981 (depending on who’s doing the math) are legal. That is because immigrants who came in illegally before then were offered amnesty through the Immigration Reform and Control Act of 1986.

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