Efforts by DHS to Estimate Southwest Border Security between Ports of Entry
https://www.dhs.gov/sites/default/files/publications/17_0914_estimates-of-border-security.pdf
Describes an array of indicators being tested by federal authorities to develop better estimates of the number of illegal border crossers. For each indicator, the report summarizes available data sources and techniques, explains the measures strengths and limitations, and presents available data. From the Office of Immigration Statistics of the Department of Homeland Security