The US is not "exporting" anything. PhDs are people, they pay for their education and they leave.
Nevertheless responding to your question:
>Contrary to common perceptions, US technology benefits from these graduates' work even if they leave: though the US share of global patent citations to graduates' science drops from 70% to 50% after migrating, it remains five times larger than the destination country share
Nevertheless responding to your question:
>Contrary to common perceptions, US technology benefits from these graduates' work even if they leave: though the US share of global patent citations to graduates' science drops from 70% to 50% after migrating, it remains five times larger than the destination country share