The method used by the scientists behind the study, from Columbia University and the Norwegian Institute of Public Health, was pretty simple. It looked at 27 countries and analyzed cognitive performance data for men and women aged between 50 and 93 from all of them. The men and women were given some cognitive tests: one where they were given a list of 10 words and then asked to recall them immediately, and another which asked them to name as many animals as possible in 60 seconds. The first one tests for episodic memory, which is memory based in experience, while the second looks at executive function, which is part of the brain's "higher" levels of functionality and involves planning, focus and working memory (memory that acts as a short-term holding bay for information). Both are pretty universal indicators of brain performance.
They also examined the countries themselves and their histories of gender equity and women's rights. The male and female participants also had to tell the scientists how much they agreed with the statement, "When jobs are scarce, men should have more right to a job than women," to see what their own ideas about gender equality might be.
The results were intriguing: the more gender-equal the country was, the better women did on the cognitive tests compared to men. In the most equal countries, women did better than men.
Why did the study look at older men and women? They've had the most exposure to their society's structures and life experience in general, from education to having kids to starting businesses and having illnesses. And that, according to the scientists, seems to add up. "Cognition in later life," they wrote, "cannot be fully understood without reference to the opportunity structures that sociocultural environments do (or do not) provide."
This isn't the first study of its kind. In 2014, a study published in the Proceedings of the National Academy of Sciences USA looked at cognition in Northern Europe, where Scandinavian countries operate on famously gender-equal lines. It focused particularly on math and science, and found something interesting: previously, scientists had thought that the gap between genders in those subjects would simply close as equality gained traction. However, as Northern Europe became more equal, the study found, women started to do better in some cognition tests than men, and virtually eliminate any gaps in others. The scientists behind that study thought that women benefit more from the sort of societal shifts that create equality than men, allowing them to leapfrog male test subjects.
This new study took that idea, and showed that it applies beyond Northern Europe, across a huge range of countries. Essentially, it proposed a global rule: the more gender-equal a country is, the better women will do on cognitive tests of specific brain functions, to the point where they outperform men.