Walls Work

A Border Patrol agent at the U.S.-Mexican border in Nogales, Ariz., January 2017. (Lucy Nicholson/Reuters)
A new study finds that fencing along the southern border has deterred illegal immigration.

NRPLUS MEMBER ARTICLE W e have a problem with people crossing the southern border on foot without authorization. But who could have guessed that putting a wall in their way would stop them?

Well, pretty much every immigration restrictionist. But a new study from American Economic Journal: Applied Economics finds that, indeed, border fencing reduces illegal immigration.

The effects are not small. “Construction in a [Mexican] municipality reduces migration by 27 percent for municipality residents and 15 percent for residents of adjacent municipalities”; it also reduces migration from municipalities that are farther away but historically have relied on the fenced area as a crossing point. Border-wall construction disproportionately deters lower-skilled workers, though it does cause some to cross the border elsewhere instead.

To reach these conclusions, the economist Benjamin Feigenberg had to assemble an impressive amount of data from numerous sources. Congress authorized the construction of nearly 700 miles of pedestrian fencing in 2006, but incredibly, there is no centralized database of where and when fencing was actually built. Pulling together the details meant searching news stories, government documents, and contracts, as well as interviewing Sierra Club staff who are tracking the fence’s progress for environmental reasons.

What the study does, essentially, is match those patterns of fence construction with trends in four other data sources.

First, a Mexican survey asks respondents if any members of the household have entered the U.S. recently. There are typically about four migrations per 1,000 respondents; as mentioned above, fence construction cuts that by about a quarter in these municipalities and 15 percent in bordering ones — likely owing to the “increase in the risk of apprehension for those who would attempt to climb over new fencing, as well as by the increase in mortality (and perhaps apprehension) risk faced by migrants who choose to go around the fence and cross in remote, topographically inhospitable border segments where border fencing was more likely to be delayed.”

A second Mexican survey collects specific details about illegal border crossings from migrants. From these data, Feigenberg discovers that fencing causes substitution: When an area is fenced, those choosing to cross the border become 57 percent less likely to do it there.

Third, a survey here in the U.S. can be used to roughly estimate the population of illegal immigrants, though it does not ask directly about immigration status. Here, Feigenberg finds that fence construction in a given region of the border “reduces the share of potentially undocumented migrants who arrived in the past year by 38 percent,” though the effect on the overall population of illegal immigrants is unclear. This could happen simply because the data are noisy, or because “migrants postpone either temporary or permanent return migration to Mexico” when there’s fencing.

But fourth, there’s a Mexican program that gives ID cards to Mexican citizens living illegally in the U.S. Fencing “induces a lagged decline in applications” for this program from folks who came from the fenced areas, “with a net decrease of 17.8–22.8 percent over the 2007–2012 period.” The data “imply a 4.2–5.0 percent decline in the potentially undocumented population in response to an additional year of fence construction exposure.”

To be sure, fencing can’t solve the illegal-immigration problem by itself: Even a fence across the entire border wouldn’t end illegal crossings, and about 60 percent of illegal immigrants overstay legal visas rather than cross illegally to begin with. But fencing does seem to be an effective way of reducing the problem it’s meant to deal with.

As for the costs, Feigenberg estimates that “roughly 5,670 border municipality migrants and 85,810 non-border migrants would be deterred each quarter if the entire border was fenced,” and that fencing costs maybe $1,325 to $1,870 per deterred migrant. Whether that’s worth it is a subjective question, though it bears noting that this is about the same as the cost of stopping one migrant via increased Border Patrol activity. Not to mention that Mexico is going to pay for the wall anyway, if that’s still a thing.

You wouldn’t think it would take a complicated analysis employing five different data sets to show that putting obstacles in people’s way can stop them from getting where they want to go. Nonetheless, it’s nice to have it.

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