The Nature Index attempts to objectively measure the scientific output of institutions and countries, taking into account differences in quality. Therefore, only articles published in 82[note 1] selected high-quality journals are counted. These journals are selected by an independent committee. If authors from several institutions and/or countries are involved in a scientific article, it is divided accordingly, assuming that all researchers were equally involved in the article. For example, this “fractional count” (FC) received by each author would be 0.1 for an article with 10 authors. If an author is affiliated with more than one institution, that author’s FC is then subdivided equally across their affiliated institutions. The process is similar for countries and regions, though the fact that some institutions have overseas labs makes the process more complicated, with such labs being counted towards their appropriate host countries.[4][5]
https://en.wikipedia.org/wiki/Nature_Index
China has so many STEM majors that a large portion of the top research being done in the US/Europe are Chinese immigrants.