How hard is it for migrants to cross the southwest border illegally and enter into the United States? That question has long been difficult to answer, but it is one that has become more urgent as Congress prepares once again to consider a broader immigration reform. A new report from the Government Accountability Office gives a surprising assessment – that it appears to have become far more difficult than most Americans realize.
The GAO report is the first to assess the number of successful illegal entries across the border using a method called "known illegal entries," or "known flow" for short. The number of illegal entries is the key statistic that matters in the debate over border enforcement. The U.S. government has for many years reported the number of "apprehensions" at the border – arrests of those attempting to enter illegally. Last year, that number fell to 327,000 at the southwest border, the lowest since 1972. While the decline in apprehensions from its 2001 peak of more than 1.6 million certainly suggests that many fewer people are trying to cross illegally, it tells us nothing definitive about the numbers who are still successfully evading the Border Patrol between the ports of entry and entering the United States.
"Known flow" is one method for trying to get at this problem. For many years, Border Patrol agents in each of the nine southwest border sectors have collected and compiled data on illegal migrant activity in their sectors. These data include actual apprehensions, but also, estimates made by agents of the number of individuals who made an effort to cross illegally but then thought twice and returned to the Mexican side ("turn backs"), as well as estimates of those who evaded capture and entered the United States successfully ("got aways"). The "got away" number is a combination of individuals who were actually observed but not arrested, and evidence compiled from "sign cuttings," which are footprints in the desert, broken vegetation, litter, and other clues that help the Border Patrol monitor incursions. These data are then compiled in what is known as the Border Patrol Enforcement Tracking System, or BPETS for short.