President Obama's director of the National Economic Council, Lawrence Summers, made no friends among women when, as president of Harvard, he tried to have a discourse about gender differences in the higher levels of math-intensive fields.    He quickly learned that speculation and conjecture are best left to philosophy undergraduate classes and actual women in academia don't much care what he thinks about their abilities.

'Girls can't do math' quickly became associated with his name but he managed to resurrect his standing nicely by becoming part of the Obama camp - however, the issue did not die.   While no one realistically believed girls had less ability to do math (and studies show there is no gender difference) the fact remained there were few at higher levels, so some more militant people invented ways that society was still keeping women down - including the odd claim that women might be afraid they will get stereotyped so they stereotype themselves.

Overall, there are now more PhDs granted to women than men so it isn't science that is a blockage but a new analysis says choice factors into it;   many women just seem to prefer biology, for example, the same way many women prefer building strategy games versus warfare ones, but there are also 'constrained' choices, like that the difficult first years as a professor coincide with the time when many women want to have children. 

Stephen Ceci and Wendy Williams of Cornell University say that in math-intensive fields like physics, electrical engineering and chemistry, 
only 16% of tenure-track positions in the top 100 U.S. universities are held by women. 

Girls' grades in math from grade school through college are as good as or better than boys', and women and men earn comparable average scores on standardized math tests, though twice as many men as women score in the top 1% on tests such as the SAT-M. 

One thing Williams and Ceci did rule out was sex discrimination - it's just the opposite today.  One large-scale national study found that women are more likely than men to be invited to interview for and to be offered tenure-track jobs in math-intensive STEM fields.    And there could be a timing factor.    Researchers are staying active longer and, since they have tenure and in the past those fields were male dominated, there are fewer open tenure jobs, leading to a lower average number of women than social or life sciences.

Williams and Ceci think the problem is that women actually choose not to go into math-heavy fields or drop out once they have started. "When you look at surveys of adolescent boys and girls and you say to them, 'What do you want to be when you grow up,' you never see girls saying, 'I want to be a physicist or an engineer,'" Ceci says. That doesn't mean they're rejecting science, but they're more likely to want to be physicians or veterinarians. 

Studies of college students find that women are more interested in organic and social fields, while men are more interested in systematizing things. And indeed, more than half of new medical doctors and biologists are women today—and in veterinary medicine, women are more than 75% of new graduates.  The same goes for social science fields, like psychology, and education.   Overwhelmingly women.

But some women do drop out of mathematics-heavy academia after receiving their degrees. While about half of undergraduate math majors in the U.S. are women, a smaller percentage go into graduate school in math and, in 2006, women earned 29.6% of math PhDs. Women are also more likely to drop out after they start a job as a professor, often because they are unable to balance childcare with the huge workload required to get tenure. Young male professors are more likely than their female counterparts to have a stay-at-home spouse or partner who takes care of children.    And perhaps women in those fields simply choose the private sector.

Williams says women are more likely to prioritize family needs. "I don't think we should try to persuade a woman who's going to be a physician, veterinarian, or biologist to instead be a computer scientist." 

But the question remains unanswered; if women are able to have the same tenure track as men in medicine or biology while juggling child-rearing, why is math a different story?

Citation: Stephen J. Ceci and Wendy M. Williams, 'Sex Differences in Math-Intensive Fields', Current Directions in Psychological Science October 2010 19: 275-279, first published on October 4, 2010 doi:10.1177/0963721410383241