Well, of course, this sort of thing is virtually never possible in the social sciences.
Nevertheless, of course studies do control for such things as much as possible. But...neither of these studies are trying to PROVE that boys and girls are equal. Rather, they are trying to DISprove the Greater Male Variability Theory, which holds that it is a biologically immutable fact that boys have more variability in their math performance and are overrepresented in both tails of the bell curve. If this is true, then it should be true universally, since it's purportedly a biological, hard-wired difference. One's nation of origin should make no difference.
I made some very rough and probably highly inaccurate bell curves for both genders based on a figures from a number of scientific studies. Some of the variables were guesses as well, so I don't have a lot of confidence in the graphs.
The graphs were interesting in that there was a mere 4% shift of the bell curves between the genders based on the numbers from US studies. If this was in any way accurate and what my graphs represented from a neurological point of view is in any way accurate, then on average, there is almost no difference in the male and female brains.
Now this small shift in the bell curves did result in a very small portion of the population being in the autism spectrum with males being significantly in higher numbers. The autism spectrum in my opinion has extreme variability in how it affect cognitive abilities. In some portions of the spectrum it can result in severe disability, whereas in other portions, it can result in extreme talents in very specific areas.
Given that males are highly represented in this spectrum, I could see this as being the cause for Greater Male Variability at the tails of the bell curve related to IQ scores.
If you have ever heard of the Male Birth Order Effect, it suggests cognitive characteristics are altered according to birth order in males. From what I have read, first born males would be shifted more toward the female side of the spectrum and later born males would be shifted more toward the male end of the spectrum. if this is true, then the bell curves for male and females would be more similar if the average family size is smaller.
So if this Male Birth Order Effect has any merit, there could be regional differences due to cultural differences affecting family sizes.
