countries as destinations. These four countries host 18 of the top 20 and 69 of the top 100 universities globally, as ranked by Academic Ranking of World Universities (the 2016 rankings are available at http://www.shanghairanking.com/ARWU2016.html).<sup>8</sup> Moreover, schooling can provide an important entry point into desired labor markets for talented individuals (Rosenzweig 2006; Grogger and Hanson 2013). Kato and Sparber (2013) show how declines in the availability of high‐skilled visas made American universities less attractive to foreign students, in terms of the number of foreign applicants and also the quality of those applicants as measured by SAT scores, compared to a handful of sending countries that were not impacted by the policy shift. Similarly, foreign students, mostly from East and South Asian countries, make up almost a quarter of the student population in Australian universities and easier entry into the Australian labor market is often cited as one of the key factors in their location choices. At later points in the educational process, Bound et al. (2015b) describe the use of graduate education in US universities to obtain access to the US labor market, and also the buffer that additional education can provide until a labor market match is realized.<sup>9</sup> Even when a labor market match occurs for skilled migrants, there is a substantial possibility of return migration—although the rate seems to vary across skill sub‐groups. The data on the subject remain limited with OECD (2008) representing an extensive effort to compile the currently available information. This report shows that 20‐50 percent of immigrants leave within five years of arriving, depending on the corridor and the time period. These levels are consistent with historical patterns; for example, Bandiera et al. (2013) find that over half of the migrants

> 8 Interestingly, different types of graduate education display varying geographic concentrations. A recent _Financial Times_ ranking of business schools included institutions from nine countries among the top 30 schools, with only 14 of the top 30 programs in the United States. Even among the top 15 business schools, seven countries are represented (http://rankings.ft.com/businessschoolrankings/global‐mba‐ranking‐2016). By contrast, the ranking of Amir and Knauff (2008) for economics PhD programs features only four countries, with the United States accounting for 24 of the top 30 departments and the United Kingdom accounting for an additional four programs. These rankings use different methodologies, so the comparisons are not precise, but the stark differences are worthy of further study.

> 9 These channels are, of course, tightly connected and build upon each other. Exceptional students are attracted to the frontier of knowledge creation, where they can themselves contribute throughout their careers to further innovations within and outside of academia. Even if pursuing purely commercial activities, these migrants can continue to promote the system through tax revenues, creating robust labor markets for graduating students. If a location starts to lose its frontier advantages, however, it may then become less attractive to future generations, which in turn further distances it from other attractive choices.

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