Prosperous nations with high gender equality have a lower percentage of women studying science, technology, engineering and mathematics (STEM), according to a new study.

Researchers from Leeds Beckett University and the University of Missouri found that countries such as Finland, Norway and Sweden - which have higher levels of gender equality - have a smaller proportion of women taking up STEM subjects when compared to countries like Algeria and Albania.

They speculate that this 'gender equality paradox' could be explained by a variety of factors.

For the study, published in the journal Psychological Science, the team examined data from 475,000 adolescents in 67 countries or regions.

They found that boys' and girls' achievement in STEM subjects was roughly similar, although science was more likely to be boys' best subject. Even when girls' ability rivalled or exceeded that of boys, they tended to score better overall for reading comprehension, which is linked with higher ability in non-STEM subjects. Furthermore, girls reported lower interest in science subjects.

These variations appeared to be common across all the regions studied and could help explain the gender disparities.

"The further you get in secondary and then higher education, the more subjects you need to drop until you end with just one," said Gijsbert Stoet, Professor in Psychology from Leeds Beckett University.

"We are inclined to choose what we are best at and also enjoy. This makes sense and matches common school advice. So, even though girls can match boys in terms of how well they do at science and mathematics in school, if those aren't their best subjects and they are less interested in them, then they're likely to choose to study something else."

The researchers think that "broader economic factors" may also be contributing to these trends. For example, less gender equal nations tend to have less welfare support, making financially rewarding STEM careers more popular for women in those places.

"STEM careers are generally secure and well-paid but the risks of not following such a path can vary," Stoet said. "In more affluent countries where any choice of career feels relatively safe, women may feel able to make choices based on non-economic factors. Conversely, in countries with fewer economic opportunities, or where employment might be precarious, a well-paid and relatively secure STEM career can be more attractive to women."

When economic concerns are lessened, like in more gender equal countries, personal preferences are more strongly expressed, according to David Geary from the University of Missouri.

"In this situation, sex differences in academic strengths and occupational interests more strongly influence college and career choices, creating the STEM paradox we describe," Geary said.

The new findings could help to increase participation in STEM, after decades of little change. For example, they suggest that targeting all girls may be a waste of time. Instead, it may be better to focus on those for whom science and maths are their best subjects and who enjoy it, but still don't choose it as a career path.

"If we can understand their motivations, then interventions can be designed to help them change their minds," Stoet said.