The E¤ects of Border Enforcement on MigrantsBorder Crossing Choices: Diversion or Deterrence?1

Illegal migration from Mexico into the United States has long led to discussions of the proper form of enforcement along the border. Past border enforcement expansion has targeted speci…c sectors rather than across the board budget increases. We assess the implications of this pattern by examining how Mexican immigrants have responded to sector-speci…c expansions in border enforcement. We estimate how many immigrants are deterred from migrating and remain in Mexico, and how many migrants are diverted to crossing at other sectors of the border. While the popular press and anecdotal evidence point towards the existence of a strong diversion e¤ect, the magnitude of this e¤ect has yet to be estimated. Using micro level data on the decisions of Mexican migrants, we employ a discrete choice model to estimate the causal e¤ects of increased enforcement on migration patterns. The causal e¤ect of enforcement on crossing decisions is identi…ed using a new set of instruments for border enforcement that vary both cross-sectionally and across time. The implied substitution patterns of our model allow us to decompose an overall e¤ect of enforcement on migration into a diversion and deterrence portion. We …nd there to be a signi…cant diversion e¤ect, and we explore the policy implications of this …nding.