Steve Hsu's calculation of geniuses in China On his blog, physicist Steve Hsu wrote the following:

Assuming a normal distribution, there are only about 10,000 people in the US who perform at +4SD and a similar number in Europe, so this is quite a select population (roughly, the top few hundred high school seniors each year in the US).
If you extrapolate the NE Asian numbers to the 1.3 billion population of China you get something like 300,000 individuals at this level, which is pretty overwhelming.

Can you explain Steve's statement in plain English – to non-statisticians using only common arithmetic operators like $+$, and $-$?
 A: Steve Hsu is using the augmented 68–95–99.7 rule to calculate what fraction of the population lies within 4 standard deviations of the mean, assuming IQ has a normal distribution.
Given how these tests are constructed, the mean IQ is around 100 with standard deviation of 15. Standard deviation is a standard measure of spread for data (denoted by the Greek letter $\sigma$). If it is small, everyone's score will be clustered tightly around $100$. If it is large, scores will be more dispersed.
Using the Wiki table linked above, we can see that about 0.999936657516334 of the population will have IQ between $100-4 \cdot 15=40$ and $100+4 \cdot 15=160$ (plus or minus 4 standard deviations from the mean). That leaves $$1-0.999936657516334=0.00006334$$ with scores below 40 and above 160. We only care about geniuses, so that gets cut in half to $0.00003167$ (since the distribution is assumed to be symmetric). If the US has a population of 322 million, that gives us $0.5 \cdot (1-0.999936657516334) \cdot 322,000,000 = 10,198$ geniuses.    
To get the Chinese numbers, he's assuming that they have the same standard deviation, but a mean that is $0.5$ standard deviations higher (so $107.5$). This is grounded in the NE Asian PISA tests results, which are more of a scholastic achievement test rather than a test of IQ. The two assumptions are that achievement score distribution looks like the IQ distribution and that the Chinese resemble NE Asians.    
Assuming this is the case, this means that to make it over 160, you only need (160-107.5)/15=3.5 standard deviations instead of 4. Using the 3.5 $\sigma$ row in the Wiki table, this gives $$0.5 \cdot (1-0.999534741841929)\cdot 1,300,000,000=302,418$$ geniuses, which is fairly close to SH's estimate.
