## Taller -> (on Avg) More Intelligent?

The NCDS contains

*a population*

*n*= 17,419), and has followed them throughout their lives for more than half a century. The NCDS also has one of the best measures of general intelligence in all of survey data. They measure intelligence at age 7 (with four different cognitive tests), at age 11 (with five different cognitive tests), and at age 16 (with two different cognitive tests). Note that the respondents are largely before puberty at ages 7 and 11, but largely after puberty at age 16.

Here are the graphs that chart the mean IQ of the NCDS respondents by sex at ages 7 and 11, before puberty. You notice that girls are slightly but (given the large sample size) statistically significantly more intelligent than boys at both ages. At age 7, the mean IQ for girls is 100.6 while the mean IQ for boys is 99.4. At age 11, the mean IQ for girls is 100.4 while the mean IQ for boys is 99.6.

However, the sex difference is reversed at age 16, as the following graph shows. Post puberty, the mean IQ for girls is 99.2 while the mean IQ for boys is 100.8. Remember, these are the same individuals who are tested at three different ages in their lives. (And, no, it does not mean that girls become less intelligent after puberty in any absolute terms. The IQs are calculated and normed at each age separately. It only means that girls become less intelligent *relative to boys* after puberty.)

Because of their faster rate of maturity, girls are more intelligent than boys until puberty, but the male advantage in intelligence emerges when boys are fully mature and *become taller than girls.*