I think the population density was one of the points. The current system allows countries to pick the schools within a selected region, and in a high population

I think the population density was one of the points. The current system allows countries to pick the schools within a selected region, and in a high population region they can focus on top performing schools. > that the sampling done on mainland China (Beijing, Jiangsu, Guangdong and Shanghai) and other cities was not taken from a wide variety of schools. Rather, the very best schools were chosen and the very best students were cherry-picked from those schools. So this is more than just focusing on Massachusetts, this is picking only the best students from the best schools in Massachusetts.