Saturday, January 07, 2012

Does earlier menarche explain the growing girl-boy academic gap?

Firstly, the age of menarche in Western nations has been declining...

Secular trends in age at menarche... [Paediatr Perinat Epidemiol. 2011] - PubMed - NCBI

Menarcheal age decreased over time in Western countries until cohorts born in the mid-20th century. It then stabilised, but limited data are available for recent cohorts. Menarche data were collected retrospectively by questionnaire in 2003-10 from 94,170 women who were participating in the Breakthrough Generations Study, aged 16-98 years, born 1908-93 and resident in the UK. Average menarcheal age declined from women born in 1908-19 (mean=13.5 years) to those born in 1945-49 (mean=12.6 years). It was then stable for several birth cohorts, but resumed its downward trend in recent cohorts (mean=12.3 years in 1990-93 cohort). Trends differed between socio-economic groups, but the recent decline was present in each group. In conclusion, menarcheal age appears to have decreased again in recent cohorts after a period of stabilization….

Surprisingly, we don't have good recent data - this is the best I could find.  There's no evidence of a similar shift in males.

Secondly, in athletics, we know a maturational advantage of a few months can make a big difference in competitive events.

High school education is a competitive event. So, if girls are maturing earlier, how does this impact their academic performance relative to boys? Does this explain why our middle and senior high school honor role events are all female? Do boys get discouraged because they can't compete?

Seems like an interesting question. I'm thinking an 'all boy' school might be a good idea for our middle son.


swiftone said...

Yes, yes, yes, if the point of school is academics, and my experience is that few folks have my values (at least where I live and worked), repeating, if the point is the academics, then by all means a single sex institution. I taught it what was likely the very last public girls school. I wish like h*** I'd had the resources to get my two younger daughters into all girls school. So far all I've done is make the claim, but the social scene so overwhelms the academic in middle and high schools with both sexes that the kids may social geniuses, but they're uneducated boars. (That looks like the wrong word... but I'm not going to be able to post this anyway. WV is not working on the ipad.)

JGF said...

Looks like WV worked a bit!

I know you meant boors. I must say though, that uneducated boars is a fantastic visual image. My son is more the boar type.

Anonymous said...

It is very hard to separate out the issue of physiological development from the literal time element in this context. It is true that the oldest students in a given grade are also likely to be the most academically successful (I've heard of studies to this effect). This follows them throughout their school career.

It is most likely that this due to an initial benefit in the first couple of years and feedback effects as they move through the school system.

However, if you compare two kids who are entering the same Kindergarten class at either end of the cutoff date, there is both a year of physiological development and a 20% difference in how much preparation time they've had. The older pupil has had an extra year of practice in every skill from reading to math to motor control. This is a huge advantage above and beyond any physiological effects.

Since your post is exclusively about physiological development differences, it is crucial that you make this distinction and can establish a physiological link between performance and development rather than one of time + feedback effects.

It is also clear that you are falling into the non-statistically-minded trap of seeing a difference in the mean between two groups and then proposing using group membership as a proxy measure for the trait in question. If physiological development follows a different schedule *on average* between boys and girls, the solution is not to have boys schools and girls schools. The solution is to have schools/grades based directly on the measure of physiological development.

This is true both on a large scale and on a small scale. If you cannot get society to accept direct use of physiological development measures, then you should do what you can to make sure that your child is one of the older members of their grade. That is likely to be much more directly effective than looking around for proxy-measures.

JGF said...

That's a very thoughtful response, but I think it missed the key point. It's primarily speculative by the way, I'm mostly curious.

I'm thinking in terms of biological ages.

Consider a boy and girl both born 7/1/1959.

In 7/2/1971 they are both biologically 12.

Now consider a boy and girl born 7/1/1989.

In 7/2/2001 the boy is stil biologically 12, but the girl (advanced menarche) is, by 1971 standards, now 13.

So it's the equivalent of all girls being born earlier.

Anonymous said...

But recall that we are talking about mean biological development. If there is indeed a process which is speeding biological development in girls but not boys, that process is not affecting all boys and girls equally.

So it may be true that at age 12, most boys are less developed biologically than most girls. However, these would be distributed on two (presumably normal) curves with a lot of overlap.

If you use gender as your proxy for development, you will have a lot of false positives (girls who don't reach menarche until a year or two later) and false negatives (boys who are going through puberty earlier than most of their peers).

So, even if your speculation about menarche being linked to mental development is true, using gender as a proxy is a much worse idea than directly measuring physical development in some way (derivative of height curve, say), and using that directly.