In Nick Robinson’s BBC documentary “The Truth About Immigration” aired today, there was an interesting mention of the government’s objective being to reduce *net* migration to “the tens” of thousands. Net migration is obtained by computing two very large figures: the number of people who arrive in the country minus the number of people who leave the country. The interesting thing is that the kind of immigration clampdown that seems to please voters can actually have the opposite effect than the one intended because it reduces the number of people who leave the country. Ezra Klein had a blog post last August reporting on Doug Massey’s research which precisely made this point about the US-Mexico Border:

“According to Massey, the rise of America’s large undocumented population is a direct result of the militarization of the border. While undocumented workers once traveled back and forth from Mexico with relative ease, after the border was garrisoned, immigrants from Mexico crossed the border and stayed. “Migrants quite rationally responded to the increased costs and risks by minimizing the number of times they crossed the border,” Massey wrote in his 2007 paper “Understanding America’s Immigration ‘Crisis.’” “But they achieved this goal not by remaining in Mexico and abandoning their intention to migrate to the U.S., but by hunkering down and staying once they had run the gauntlet at the border and made it to their final destination.” The data support Massey’s thesis: In 1980, 46 percent of undocumented Mexican migrants returned to Mexico within 12 months. By 2007, that was down to 7 percent. As a result, the permanent undocumented population exploded.

This is based on this paper.