The performance of boys and girls in school is much more similar in science, technology, engineering and mathematics (STEM) subjects than in other disciplines. That is according to an analysis carried out by researchers in Australia of the grades of over 1.6 million students around the world. The authors say that their study disproves the “variability hypothesis”, which suggests that male over-representation in STEM careers comes from a greater variability in grades among boys than girls (Nature Communications 9 3777).

Led by biology PhD student Rose O’Dea from the University of New South Wales, the researchers examined 227 studies of student grades that were carried out between 1931 and 2013. They looked at the variability – defined as the width of the distribution curve – of exam results between girls and boys and found that the biggest differences were in non-STEM subjects. Here they found that the mean grades of girls were 7.8% higher than boys and 13.3% less variable. In STEM subjects, however, these figures were roughly halved: girls grades were 3.1% higher and 7.6% less variable than boys.

People in general seem to continue to believe that the gender gap’s origins are biological, rather than the effect of compounding stereotypes Lara Perez-Felkner

By analysing the grade distributions, the researchers found that the top 10% of grades in STEM subjects had an equal gender ratio, while non-STEM subjects were female-heavy. “Our results support greater male variability in academic performance, but they don’t support gender differences in variability as an explanation for gender differences in workforce participation because we find the smallest gender differences in variability in maths and science,” O’Dea told Physics World.

Top of the class

The authors say their work disproves the variability hypothesis, which is often – mistakenly as it turns out – said to be the reason why boys outnumber girls at the top of the class, despite girls achieving higher average grades. “Greater male variability was first written about in the 1800s as an explanation for why the geniuses and fools in society were men,” says O’Dea. “Since then women have had greater access to higher education and girls are now out-performing boys at school on average, but women are still under-represented in maths-intensive fields. The variability hypothesis is now used to explain this discrepancy.”

O’Dea adds that the study highlights gender differences in humanities as one possible reason why fewer females opt for STEM careers. In STEM, girls face more male competition, she says, along with negative gender stereotypes and the challenges of trying to succeed in male-dominated workplaces. This means, she thinks, that STEM can be a riskier option for girls compared to boys. “There is also some evidence from other studies that students who are good all-rounders – who get high marks in both language and maths – are less likely to stick with STEM, regardless of their gender,” says O’Dea, adding that working on increasing boys’ language skills could be another way to reduce the STEM gender gap because this is the area with the biggest gender differences. Read more Gender gap in physics among highest in science

“Despite its limitations, scientists and people in general seem to continue to believe that the gender gap’s origins are biological, rather than the effect of compounding stereotypes and signals young people get towards and away from STEM careers depending on their gender identity,” Lara Perez-Felkner, a sociologist at Florida State University in the US told Physics World. “While this study does not singularly disprove [the variability] hypothesis, it sheds further doubt on its significance. If mathematical ability variation is so important, we would see no variation across nations. Biology should look the same everywhere. Rather, we see a considerable amount of variation by country.”