Overstay Enforcement: Additional Mechanisms for Collecting, Assessing, and Sharing Data Could Strengthen DHS's Efforts but Would Have Costs, Report to the Committee on Homeland Security and Governmental Affairs, U.S. Senate [open pdf - 2MB]
"According to Pew Hispanic Center estimates, approximately 4 million to 5.5 million unauthorized immigrants in the United States entered the country legally on a temporary basis but then overstayed their authorized periods of admission--referred to as overstays. As requested, GAO [Government Accountability Office] examined the extent to which the Department of Homeland Security (DHS) (1) takes action to address overstays and its reported results; and (2) identifies overstays and shares this information among its border security and immigration enforcement components. GAO reviewed relevant documents, such as standard operating procedures, DHS guidance, and overstay investigations data from fiscal years 2006 through 2010; interviewed officials from DHS components; and visited 6 DHS field offices and 12 ports of entry based on geographic dispersion, among other factors. The results of these visits are not generalizable, but provided insights into DHS operations. [...] GAO recommends, among other things, that DHS establish a time frame for completing overstay enforcement planning, performance measurement mechanisms, and, if benefits outweigh costs, a mechanism for collecting departure forms at land borders and alerts for additional categories of overstays. DHS concurred with our recommendations."
Government Accountability Office: http://www.gao.gov/