Half of the poorer rural area kids have IQ 90 or below? Chinese rural popn is about 40% of total, lets assume 20% belong to the poorer rural area and the average IQ there is 10 points lower(due to economic reasons), say at IQ 95 (and the S.D. is about 13) and 50% of them are below IQ 95, better than the article's claim 1/2 are below IQ 90. There's a math formula on the distribution curve and one can check it out