Chinese and Chinese-American winners of the Putnam contest

Factual Questions
1

The Putnam competition is a mathematical contest for the very best college undergraduate math students.
In recent years the highest scorers have been overwhelmingly Chinese and Chinese-Americans.

  1. What percent were, over the past few years, Chinese and what percentage were Chinese-Americans?
  2. Over the past few years, of those who were Chinese (and not Chinese-Americans) what percentage remained in the U.S. after college (and grad school) and what percentage returned to China?
    I realize the answers must be estimates, but they would be helpful.
2

In 2017, they sound like they were almost all east asian.

https://kskedlaya.org/putnam-archive/putnam2017results.html

Not as much in 2015 and 2016, but still a strong showing.

https://kskedlaya.org/putnam-archive/putnam2016results.html

https://kskedlaya.org/putnam-archive/putnam2015results.html

3

This may help some.

4

The 2017 Putnam Fellow [Ömer_Cerrahoğlu](Omar (name) - Wikipedia Cerrahoğlu) is Romanian.

The 2017 Putnam Fellow Jiyang Gao is Chinese.

Since many Putnam Fellows are former International Math Olympiad winners, you might be able to track down the nationalities of some others from IMO records.

Considering that the overall winners of the Putnam competition make up only a minuscule fraction of even the top-ranked college mathematics students (and several of them win in multiple years), I’m not sure how much difference it makes where this tiny handful of math whizzes go after graduation.

For a big-picture comparison, nowadays about 8 in 10 Chinese students return to China after studying abroad.