Important new research concludes immigration restrictions that prevent companies from hiring high-skilled foreign nationals in the U.S. represent bad economic policy and are counterproductive. “When we aggregate at the national level, inflows of foreign STEM [science, technology, engineering and math] workers explain between 30% and 50% of the aggregate productivity growth that took place in the United States between 1990 and 2010,” according to economists Giovanni Peri (UC, Davis), Kevin Shih (RPI) and Chad Sparber (Colgate University).