Why U.S. immigration matters for the global advancement of science
利用国际数学奥林匹克竞赛参与者数据，研究发现移民到美国的天才青少年生产率是移民到其他国家的六倍，且全球顶尖青年中三分之二希望赴美读本科，但仅四分之一成行，资金约束是主要障碍。
While the impact of U.S. immigration on innovation in the U.S. has been well-studied, less attention has been paid to the relationship between U.S. immigration and global innovation. This paper fills this gap using novel data on a set of highly talented teenagers— participants in the International Mathematical Olympiad (IMO)—and presents three results. First, migrants to the U.S. are up to six times more productive than migrants to other countries, even after accounting for talent during one's teenage years. Second, most of the productivity difference is associated with academics being more productive in the U.S. compared to those who stay home (with differences in entry rates into academia mattering less). Third, there is a large gap between aspirations to move to the U.S. and actual migration: about 2 in 3 of the world's most talented youth from developing countries would like to migrate to the U.S. for their undergraduate studies, but only 1 in 4 do, with financing constraints being a key barrier. A back of the envelope calculation suggests that removing constraints on immigration could increase the global scientific output of future cohorts by up to 50 %.