There really is no difference between men and women's math abilitiesS

There's a longstanding myth of a gender gap between boys' and girls' math performance, suggesting some basic biological difference in how the two genders approach math. It's deeply controversial and widely discredited. And now, a new study has completely debunked it.

Until now, there was maybe a sliver of statistical data to support the existence of this gender gap — nothing remotely convincing, mind you, but just enough that the idea couldn't be entirely dismissed out of hand. While most who studied the issue pointed for cultural or social reasons why girls might lag behind boys in math performance, there was still room for biological theories to be proposed.

The best-known of these is the "greater male variability hypothesis", which basically says ability among males varies more widely than that of females, which means you'll see more males at the extreme ends of the spectrum, good and bad. Then-Harvard president Larry Summers infamously put forward this idea back in 2005 as a way to explain the lack of great female mathematicians, and this was one of about a dozen different factors that ultimately cost him his job.

Now, researchers Jane Mertz of the University of Wisconsin-Madison and Jonathan Kane of the University of Wisconsin-Whitewater have performed the most comprehensive exploration yet of math performance. They took in data from 86 different countries, many of which had not previously kept reliable records of math performance and so their addition allowed for much stronger cross-cultural analysis. So what did they find?

First, in many countries, there's no gender gap at all both at the average and very high levels of performance. Some countries, including the United States, do show a gender gap, but that gap has decreased substantially over the last few decades, and some test scores suggest American girls have already caught up to their male counterparts.

The researchers looked at one measure of young people with extremely high math abilities - namely, those who scored a 700 or higher on the math section of the SAT before the age of 13. In 1970, boys in this category outnumbered girls 13 to 1, while today the ratio is just 3 to 1 and still falling. Similarly, while just 5% of math Ph.D.s in the United States in the 1960s were given to women, today that figure stands at 30%.

All of these findings argue strongly that the apparent gender gaps are really just disparities in education and cultural expectations, not evidence of some deeper biological mechanism. If there really is a "math gene" or something like it that males have and boys don't, we simply wouldn't see such vast changes over time or indeed in different countries, many of which show no gender gap at all.

And what about the greater male variability hypothesis? Well, there's a bit of evidence to support this - provided you blatantly cherry-pick certain countries. Kane and Mertz compared the variability of male and female math scores in different countries and found that the variability ratio in Taiwan is 1.31, meaning boys there do have substantially more variability than girls.

However, the ratio in Morocco is 1.00, meaning there is absolutely no difference in the genders' variability. You can go even further by looking at Tunisia, which has a ratio of 0.91, which means it's actually the girls there who show greater variability. For this hypothesis to be correct, it would have to hold true for all countries — the fact that the ratios vary so much means it's just the result of different cultural factors, or it could simply be random statistical noise.

Mertz and Kane were also able to debunk a couple other hypotheses about math performance, specifically the "single-gender classroom hypothesis" and "Muslim culture hypothesis", both of which were argued for by Freakonomics author Steven Levitt. The idea here is that the gender inequity found in many Muslim countries actually benefits girls, perhaps because they are generally educated in gender-separated classrooms and that helps somehow.

It's an interesting, counter-intuitive idea, but it also appears to be completely wrong. The authors say that, upon close examination of the data, girls in these single-gender classrooms still scored quite poorly. The boys in these countries, such as Bahrain and Oman, had scored even worse, but Kane suggests that's because many attend religious schools with little emphasis on mathematics.

Also, low-performing girls are often pressured to drop out of school and so don't appear in the statistics, which falsely inflates the girls' overall performance. The point, says Kane, is that these differing scores don't point to benefits of gender-separated classrooms or speak to features of Muslim culture as a whole - rather, they're due to social factors in play in a few countries, and the single-gender classrooms are just a confounding variable.

Indeed, Mertz and Kane were able to demonstrate pretty much the exact opposite of those hypotheses: as a general rule, high gender equality doesn't just remove the gender gap, it also improves test scores overall. In particular, countries where women have high participation in the labor force, and command salaries comparable to those of their male counterparts, generally have the highest math scores overall. The researchers comment on this finding:

Kane: "We found that boys — as well as girls — tend to do better in math when raised in countries where females have better equality, and that's new and important. It makes sense that when women are well-educated and earn a good income, the math scores of their children of both genders benefit."

Mertz: "Many folks believe gender equity is a win-lose zero-sum game: If females are given more, males end up with less. Our results indicate that, at least for math achievement, gender equity is a win-win situation."

As for how to close the gap even further and generally increase math scores, Mertz says the study argues strongly against the proposal to create single-gender classrooms. Instead, the researchers point to fairly common sense solutions: increase the number of math teachers in middle and high schools, decrease the number of children currently living in poverty, and take greater steps to reduce gender inequity.

Those may all seem fairly straightforward, but that's pretty much exactly the point - this isn't about tricking our brains or creating some perfect conditions to unlock children's hidden mathematical aptitude. As Mertz explains, this is all about culture, not biology:

"None of our findings suggest that an innate biological difference between the sexes is the primary reason for a gender gap in math performance at any level. Rather, these major international studies strongly suggest that the math-gender gap, where it occurs, is due to sociocultural factors that differ among countries, and that these factors can be changed."

Read the original paper at the American Mathematical Society. Top image: D Sharon Pruitt/Pink Sherbet Photography, via Flickr.