lihood of crossing with a border smuggler (Singer and Massey, 1998; Massey, Durand, and Malone, 2002; Massey, Durand, and Pren, 2010).

Field data show that the vast majority of would-be unauthorized Mexican migrants—roughly 9 of 10—hire such smugglers to reduce the physical risk of clandestine entry and improve their prospects for evading the Border Patrol. The percentage of migrants using paid guides has steadily risen from the early 1990s, from around 80 percent to nearly 100 percent today (Mexican Migration Project, 2010). Not surprisingly, increased border enforcement also increases the cost of hiring a border smuggler, commonly known as a coyote (Massey, Durand, and Malone, 2002; Gathman, 2008; Massey, Durand, and Pren, 2010).

There are several reasons that the deterrent effects of enforcement are small, as shown in most studies. The most obvious is that rising enforcement at particular locations on the border simply induces migrants to cross elsewhere (Orrenius, 2004). Another reason is that as crossing costs have increased, migrants’ ability to finance crossings using their U.S.- based networks has also risen, resulting in little net effect of rising costs on the proclivity to migrate (McKenzie and Rapoport, 2007). A third reason is that, in the long term, the earnings gains from migration far outweigh border crossing costs, which also leads to little deterrent effect.

Finally, personal knowledge of border crossing and experience with worksite enforcement in the United States are positively correlated with intent to migrate, perhaps explaining the counterintuitive finding in some studies of a positive effect of enforcement on undocumented migration. Information about U.S. enforcement activities (both at the border and in the interior) continually flows from U.S.-based migrants to relatives and friends in migrant-sending communities. Having good information does not deter migration, and it may in fact increase the propensity to migrate by raising potential migrants’ confidence about their ability to circumvent barriers to illegal entry, find a better coyote, and so on (Fuentes et al., 2007; Parks et al., 2009; Hicken et al., 2010).

Other research has also noted that migration and enforcement are endogenous,8 making causal effects difficult to discern (Hanson and Spilimbergo, 1999). Field data gathered in 2007-2011 suggest that enforcement is a bigger deterrent of potential migrants when they also face a lack of jobs in the United States. This interactive effect reflects the changed calculus of expected economic returns to migration during a recessionary period. According to survey data, migrants’ perceptions of the intensity of border enforcement were essentially stable during this period. During each year of the recession, 9 of 10 potential migrants believed that it was


8Since the Border Patrol responds to increases in illegal crossings by ramping up enforcement, crossings and enforcement often appear to rise together.

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