Migrant cohort size,enforcement effort,and the apprehension of undocumented aliens

This article examines macro-structural conditions that affect time trends in aggregate probabilities of undocumented alien apprehension along the Mexico-US border. We show that the number of migrants attempting to cross the border illegally in a given period and the level of effort expended by the INS to apprehend undocumented migrants are principal determinants of apprehension probabilities. Our findings differ from those in earlier work by Donato, Durand, and Massey who argue that individual, household, and community factors are not significant predictors of apprehension probabilities and conclude that escaping INS detection at the border is essentially a random process unrelated to personal traits or to enforcement provisions of the 1986 Immigration Reform and Control Act. Although Donato et al. recognize that apprehension probabilities are affected by the size of the US Border Patrol budget and the number of personnel, they omit these larger structural factors from consideration. Instead, they introduce annual dummy variables to control for macro-structural forces. This approach is unsatisfactory because it confounds the effects of numerous explanatory factors. We conclude that one implication for future research is that it is worth modeling the effects of individuals' characteristics on apprehension probabilities by including as predictors an estimate of the flow of undocumented migrants and measures of INS border enforcement effort. Controlling explicitly for three macrostructural conditions may disclose the importance of some individual-level factors that would otherwise be obscured.