But one big question remains unanswered: Is Cotton right in claiming many Chinese students are going back to China, armed with cutting-edge training in fields like AI? The available evidence — including our research — suggests he’s not.

This strong claim is based on weak data

Cotton’s argument rests on a basic claim, also made in less confrontational ways by others in academia and government: that U.S. universities train top Chinese researchers who then return to China, and who may end up working on projects that harm U.S. economic and security interests.

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Those who fear such a brain drain typically refer to data from the Chinese Ministry of Education. This data is prominently cited in an extensive recent Senate report on China’s threat to the U.S. research enterprise, for instance. Statistics published by the ministry show eight overseas students returned for every 10 students who studied abroad in 2018, up from a ratio of just 1 in 10 in the early 2000s.

But these numbers aren’t very helpful. We don’t have any documentation on how Chinese officials gathered or analyzed the data. Even if the data were reliable, the Ministry of Education includes all Chinese students abroad — not just those in the United States. They also don’t distinguish students by degree level or area of study. The numbers thus can’t tell us much about those Cotton is especially concerned about: “postgraduate [students] in advanced scientific and technological fields.”

What the evidence tells us

Several recent studies provide a better look at this group of students. All of these studies suggest the vast majority of advanced Chinese graduates in technical fields want to — and do — remain in the United States after completing their degrees.

In a forthcoming paper, my co-authors and I analyze survey data from the National Science Foundation, which every year asks all PhDs graduating from U.S. universities whether they plan to stay in the country. Across nearly every STEM field, 85 to 90 percent of Chinese graduates intend to stay — the exception is agriculture, where few Chinese students are enrolled. As the figure below shows, these intention-to-stay rates did not decrease between 2010 and 2017, casting doubt on concerns about a “reverse Chinese brain drain.”

Other studies have looked at a longer time frame. One, by the Oak Ridge Institute for Science and Technology, tracked how many Chinese science and engineering PhD graduates were still in the United States five or 10 years after completing their degrees. They found stay rates of around 85 percent on both timelines.

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In another recent study, my co-authors and I analyze data we collected on the career histories of 2,000 recent top U.S. PhD graduates in artificial intelligence, one of the fields Cotton mentions explicitly. We found that 91 percent of Chinese PhDs in artificial intelligence remain in the country for at least five years (the point at which our data ends). And, as was true in the NSF data, we found no noticeable declines in Chinese stay rates between 2014 and 2018.

Here’s what we still don’t know

Unfortunately, we have good retention data only for PhDs. While important — especially from the perspective of groundbreaking innovation — PhD students are clearly only one part of the picture. Stay rates among bachelor’s and master’s students could very well differ from those among PhDs. We currently have no way to know for sure.

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It’s also conceivable that Chinese graduates still stay in the United States at the same rate immediately after graduation, but that recent graduates have changed their minds about remaining over the long term. We are not aware of any data source that systematically tracks how long graduates intend to stay in the United States after completing their degrees.

Finally, past trends are an uncertain guide to the future. Whether graduates continue to stay in large numbers depends in part on factors outside of their control. Immigration barriers have made it increasingly difficult to stay in the United States, especially with key visa programs such as Optional Practical Training (OPT) on the chopping block. Just because retention rates have remained high in recent years does not mean they will stay that way.

What we can say, however, is that available evidence does not support Sen. Cotton’s assertion that China’s brightest minds are heading home. In fact, as our research shows, the opposite may be true — Communist Party officials have long complained that “the number of top talents lost in China ranks first in the world.”

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To be clear, policymakers’ concerns about Chinese researchers working in high-tech fields in the United States are far from groundless. But if U.S. policy is based on mistaken assumptions about Chinese students, it runs the risk of creating more problems than it solves.

Remco Zwetsloot (@r_zwetsloot) is a research fellow at Georgetown University’s Center for Security and Emerging Technology (CSET).