is taken as evidence that a resurgence of mass unauthorized migration is unlikely (Passel and Cohn, 2012).


The steady growth of the unauthorized population in the United States during the past several decades might suggest at first glance that border enforcement has been ineffective. Conversely, the fact that the number of apprehensions and stock of undocumented migrants has decreased in more recent years might suggest that the stepped-up enforcement efforts at the border have been effective. As discussed briefly in the previous section, the incentives to engage in unauthorized migration have been changing due to economic and social changes in destination and sending areas and due to the expansion of migrant networks. An appropriate evaluation of immigration enforcement must consider a counterfactual scenario in which other migration factors are held constant as border enforcement is increased. This would indicate whether and to what extent border enforcement is a deterrent.19

Studies of migration tend to find evidence of small but significant deterrent effects of border enforcement. Gathmann (2008) found that the border buildup between 1986 and 2004 raised smugglers’ fees by 17 percent and increased the time costs of crossing by 2 to 5 additional days. Orrenius (1999) found that a 20 percent increase in the smuggling fee caused a 13 to 21 percent decline in the probability of migrating. Spener (2009) notes that enforcement operations drive smuggling prices up both by requiring migrants to buy a more complex portfolio of smuggling services than in the past and by pushing traffic to remote areas, making it harder to cross the border undetected. A number of studies have found that more border enforcement negatively affects the probability of undocumented migration after accounting for the role of other forces influencing this decision, although the size of deterrence effects in most of these studies is generally modest (Amuedo-Dorantes and Bansak, 2011; Angelucci, 2012; Cornelius and Salehyan, 2007; Hanson and Spilimbergo, 1999; Massey and Riosmena, 2010; Orrenius and Zavodny, 2005). Angelucci (2012) finds that the elasticity of illegal inflows to border enforcement is between –0.4 and –0.8 and that sensitivity to enforcement has increased over time. Amuedo-Dorantes and Bansak (2011) find that an increase of one-half million linewatch hours—the average yearly increase along the U.S.–Mexico border between 1990 and 2003—reduced intentions to re-migrate among a sample of male return migrants by about 14 percent. The deterrence effects can also be short-lived: Dávila and colleagues (2002) found that, although


19 In other words, although undocumented migration increased, it could have been even higher in the absence of increased enforcement.

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