Immigrants have been linked to greater invention and innovation in the US. According to one report, "immigrants have started more than half (44 of 87) of America's startup companies valued at $1 billion or more and are key members of management or product development teams in over 70 percent (62 of 87) of these companies." Foreign doctoral students are a major source of innovation in the American economy. In the United States, immigrant workers hold a disproportionate share of jobs in science, technology, engineering, and math (STEM): "In 2013, foreign-born workers accounted for 19.2 percent of STEM workers with a bachelor's degree, 40.7 percent of those with a master's degree, and more than half—54.5 percent—of those with a Ph.D."