It might not be super sound methodologically to only do it for US in PISA, but I don’t think that it affect results significantly. Other high performing countries have highly homogenous populations, so the aggregate score of the entire country is very close to the score of the top performing group. On the other hand, in countries with heterogenous populations like India, Indonesia, Afghanistan or Nigeria, even the top groups are not performing very well. If you know of a country other than US, where the top performing group does significantly better than country average, and their performance is on the level of, say, European average, I’d be very curious to learn about it!
The main methodological problem is how one can leave out like 40% of the United States, and say that the US comes on top (which it still doesn't!). Like, I'm not even questioning the racial split data, but selecting the two groups and saying that the US is the best is a weird flex that wouldn't pass muster in Stats 101.
I’m not leaving out anyone. What I’m saying is that each American group individually comes out out of top, relative to matching groups elsewhere, and the fact that overall we don’t, is just an example of Simpson’s paradox. American blacks and Hispanics are ahead of foreign blacks and Hispanics too, it’s not just whites and Asians.
