Garry Kasparov is arguably the best chess player in the World, and he’s an Ashkenazi Jew. Assuming there are about 10 million Ashkenazi Jews in the world, normalizing the distribution of chess skill makes Kasparov 5.2 standard deviations above the mean chess skill of his ethnic group. Given the 0.35 correlation between IQ and chess skill, Kasparov’s IQ should be 0.35(+5.2 SD) = 1.82 SD above the Jewish mean.
Assuming Ashkenazi Jews have a mean IQ of 110 (SD = 15?), this would mean an IQ of 1.82(15) + 110 = 137. Of course given the very imperfect correlation, there would be a huge amount of uncertainty around this prediction. Also, the correlation was based on chess club participants and can’t necessarily be generalized to entire ethnic groups, many members of which don’t even play chess.
Nonetheless, Kasparov was actually given an IQ test by a German magazine and he scored 135…remarkably close to the figure predicted from simple linear regression.