For years -- and especially since 2005, when Lawrence H. Summers, then president of Harvard, made his notorious comments about women's aptitude -- researchers have been searching for ways to explain why there are so many more men than women in the top ranks of science.
Now comes an intriguing clue, in the form of a test given in 65 developed countries by the Organization for Economic Cooperation and Development. It finds that among a representative sample of 15-year-olds around the world, girls generally outperform boys in science -- but not in the United States.
What explains the gap? Andreas Schleicher, who oversees the tests for the O.E.C.D., says different countries offer different incentives for learning science and math.
In the United States, he said, boys are more likely than girls to "see science as something that affects their life."
Then there is the "stereotype threat."
"We see that very early in childhood -- around age 4 -- gender roles in occupations appear to be formed," said Christianne Corbett, co-author of the 2010 report "Why So Few? Women in Science, Technology, Engineering and Math," by the American Association of University Women. "Women are less likely to go into science careers, although they are clearly capable of succeeding."
Researchers say these cultural forces are strong in the United States, Britain and Canada but far less pervasive in Russia, Asia and the Middle East, which have a much higher proportion of women in science and engineering. In Jordan, for example, girls score more than 8 percent better in science than boys do. The disparities in Albania and Qatar are almost as large.
"For girls in some Arab countries, education is the only way to move up the social structure," Mr. Schleicher said. "It is one way to earn social mobility."science
This article originally appeared in The New York Times.