Over the past decade, the U.S. Department of Homeland Security (DHS) has dramatically increased its enforcement effrorts at the U.S.-Mexico border. During this same period, there has also been a sharp decline in the number of unauthorized migrants apprehended at the border. To evaluate whether heightened enforcement efforts have contributed to reducing the flow of undocumented migrants, it is critical to estimate the number of border-crossing attempts during the same period for which apprehensions data are available.
DHS charged the panel with providing guidance on the use of surveys and other methodologies to mestimate the number of unauthorized crossings at the U.S.-Mexico border. A better understanding of the magnitude, timing, and location of these flows will help DHBS to better evaluate the effectiveness of its enforcement efforts and provide a more somplete report to the public on the state of illegal immigration. This study discusses the usefulness and limitations of U.S. and Mexican survey data, DHS administrative data, and modeling approaches (in conjunction with both survey and administrative data) for estimating flows.