Exploratory Time Series Analysis of Apprehensions and Linewatch Hours on the Southwest Border [open pdf - 470KB]
"Whether heightened border enforcement reduces future undocumented migration is a question at the heart of most policy debates on U.S. immigration reform. To address this question, most researchers utilize publicly available data on border apprehensions and linewatch hours, which serve as proxies for the flow of unauthorized migration and the underlying enforcement effort, respectively. A standard assumption of most researchers is that apprehensions are a function of linewatch hours. It is conceivable, however, that linewatch hours may also be a function of apprehensions. Although some studies recognize the possibility of a reverse relationship, the implied hypothesis-namely, that apprehensions predict linewatch hours-has not been formally tested. This paper fills the gap by providing a formal time series analysis of the historical relationship between monthly apprehensions and linewatch hours between 1963 and 2004. Overall, the findings indicate that while apprehensions and linewatch hours were strongly correlated in the same time period, past linewatch hours were not strong predictors of future apprehensions, or vice versa. This suggests that, while a strong contemporaneous relationship between linewatch hours and apprehensions exists, the two series may be less useful for forecasting purposes. Although this paper does not assess enforcement effectiveness or deterrence, the preliminary results may assist future researchers by providing empirical justification for econometric specification decisions made when studying border enforcement issues."
United States Department of Homeland Security: http://www.dhs.gov/