Fuzzy Math on Illegal Immigration

By Carl Bialik, The Wall Street Journal, April 5, 2006


New York Democrat Charles Schumer said legislation is needed "to solve the problem of millions of foreigners who live here illegally and unprotected" as well as "to alleviate the problem of the millions more who enter illegally every year." He kept his estimate of the number of illegal immigrants vague because "no one knows for sure how many are really here," the National Journal reported. "Nor can anyone give a reliable estimate of how fast that unknown figure is growing each year."

A sound bite from last week? Nope. The year was 1985, Mr. Schumer was in the House of Representatives and debate was raging over how to address the growing number of illegal immigrants, then estimated at somewhere between 3 million and 12 million.

Twenty-one years later, several amnesties granted to undocumented immigrants [criminal illegal aliens] have failed to keep the number of illegal immigrants from growing. And estimates of their numbers remain fuzzy and full of pitfalls, even as lawmakers toss them around in the latest round of debates over whether to offer guest-worker status to illegal immigrants.

At the core of the problem is the fact that undocumented immigrants [criminal illegal aliens] don't generally come forward to be counted. The most widely quoted estimate of 11 million to 12 million is derived indirectly, using what's called a residual method: Researchers subtract the number of immigrants who were authorized to come to the U.S. from the number of foreign-born residents counted by the Census Bureau, then adjust the number using estimates of immigrants' deaths and migration, and of Census undercounting.

Some critics say that estimate understates the degree of undercounting: Another estimate making the rounds holds that there are 20 million illegal immigrants.

That was the upper range Bear Stearns analysts Robert Justice and Betty Ng estimated last year, citing high growth rates in foreign remittances and in school enrollments in localities with high illegal-immigrant populations. The analysts added, "According to our discussions with illegal immigrants, they avoid responding to census questionnaires."

And there are still-higher estimates to be found online: The Web site of the "immigration crime-fighting" group American Resistance Foundation (http://www.TheAmericanResistance.com) estimates there are more than 28 [sic] million illegal immigrants [actually the estimate is up to 20 million], based largely on border-patrol apprehension rates; however, there is little reliable data on how many border-crossers who are caught trying to enter a second time....

In 2000, before it was folded into DHS, the Immigration and Naturalization Service used the residual method to estimate there were seven million illegal immigrants and their numbers were growing by 250,000 to 300,000 per year. Mr. Strassberger says that remains the government's best estimate, though he concedes it's out of date.

Following largely the same procedure that INS used, the Washington, D.C., think tank Pew Hispanic Center counted 11 million illegal immigrants last year, and between 11.5 million and 12 million last month; the group is the source for most lawmakers and reporters citing a number. (The Wall Street Journal generally has printed estimates of 11 million, or a range of 11 million to 12 million.)

But the residual method is by necessity complicated, and each step in its formula introduces uncertainty. Jeffrey Passel, a Pew senior research associate, walked me through the procedure (also outlined in Pew's latest report). The starting point is the Census Bureau's annual Current Population Survey report, which bases a count of foreign-born residents on interviews conducted with about 80,000 households. The Census intentionally seeks out a disproportionately large number of Hispanic households to get richer data. Interviewers, either by telephone or in person, ask where every member of each household was born. These figures are then extrapolated to the nation, adjusting for the larger sample of Hispanics. The latest estimate of foreign-born Americans to emerge from such calculations was roughly 36 million, Dr. Passel says.

Next, Pew subtracts the number of foreign-born Americans authorized to be in the country. Dr. Passel's team compiles annual numbers of green-card recipients, refugees and people granted asylum, a count that stretches back decades. But merely adding these numbers would be misleading, because some authorized immigrants decide to leave the country and others die. Dr. Passel assumes that immigrants of a certain age die at the same rate as the country's residents overall, and uses estimates from various studies on "outmigration," something he concedes is "hard to measure." (The outmigration numbers are also much bigger -- perhaps seven times as large -- as the number of deaths, because immigrants tend to be young.) Then the calculated total is subtracted from the total number of foreign-born residents, and the result is adjusted upwards by 10% to account for census undercounting of illegal immigrants. (That adjustment is based on one post-Census 2000 survey of undercounting among Mexican immigrants in the Los Angeles-area; other studies have yielded different estimates of undercounting.)

Dr. Passel and Robert Warren pioneered the residual method while working together at the Census Bureau in the 1980s. Dr. Warren then helped develop INS's methods for its 2000 estimate, so it's no surprise that the government's methods are similar to Pew's. Michael Hoefer, director of the office of immigration statistics, a branch of DHS, told me that the government uses the Census Bureau's American Community Survey instead of the Current Population Survey, which is based on a larger sample of households but is published later than the CPS. (Mr. Hoefer's office is working on a 2004 estimate to update the 2000 official figure of seven million.)

Also, Pew's count of illegal immigrants includes those considered "quasi-legal," meaning they're on their way to legal status... That could mean a difference of about one million in the total count, Mr. Hoefer says....

However, there is still large uncertainty in the current estimates, due largely to Census undercounting and limited data about immigrants [and illegal aliens] leaving the country....

Not everyone agrees that the numbers debate matters. "As long as people concede that the number is large to begin with and is increasing, the number itself is irrelevant," Vernon Briggs, a professor of labor economics at Cornell who favors enforcing sanctions against employers of illegal immigrants, told me....

Read the complete article.

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