2012). Net migration from Mexico was therefore zero or perhaps even slightly negative during this period, compared with net illegal migration of 2.3 million from Mexico between 1995 and 2000. Other studies suggest the rising returns occurred at the tail end of the crisis (cf. Giorguli and Gutiérrez, in press; Rendall et al., 2011). As a result of declining inflows and rising returns, the unauthorized Mexican-born population fell to 6.1 million in 2011, down from 7 million at its peak in 2007 (Passel et al., 2012).

Characteristics of the Unauthorized Population

Not all unauthorized immigrants “enter without inspection” at the border. People who overstay or otherwise violate the terms of their visas, such as by working while on a tourist visa, are also considered unauthorized. Among the unauthorized population, between 25 and 40 percent are thought to be visa overstayers, while the rest entered without inspection (Passel, 2005). The efforts of the U.S. Department of Homeland Security (DHS) to identify and report on overstays have been hindered by the absence of a comprehensive biometric entry and exit system for identifying overstayers (U.S. Government Accountability Office, 2011a).

These population estimates represent unauthorized immigrants who are U.S. residents, i.e., people living in the United States on a longer-term basis (more than 1 year). However, much, and probably most, of the undocumented flow across the U.S. border consists of Mexicans who are coming to the United States for short-term employment, including seasonal work in agriculture and construction. This distinction between longer-terms residents (“settlers”) and short-term residents (“sojourners”) is important in considering data from different sources and policies concerning immigration and admission.

Even among the settler population, many return to their home countries. But in recent years, a larger share of the unauthorized population consists of long-term residents who appear to be permanently settled in the United States (Taylor et al., 2011). Estimates suggest that about one in seven unauthorized immigrants arrived within the past 5 years, and most (almost 60 percent) have lived here for more than a decade (Hoefer et al., 2012). This pattern represents a dramatic change from a decade earlier, when about one-third of unauthorized immigrants had been in the United States for less than 5 years and a minority (44 percent) had been in the country for more than a decade (Taylor et al., 2011). Some research suggests that tougher border enforcement has played a role in reducing circular migration and inducing immigrants to permanently settle in the United States (Angelucci, 2012; Massey and Pren, 2012; Reyes, 2004). Although the typical unauthorized resident is a male aged 18-39, there are

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