The RePEc blog laments how few women register for its services. I would like to take this opportunity to ask where the women are disappearing in the profession. According to the quoted CSWEP report, 34.5% of graduating female students are female, but only 8.1% of full professors are women. There is considerable leakage.
These numbers need some qualifications, though. First, they pertain to PhD granting institutions in the US. Thus, the missing women may have moved to non-PhD granting universities along their careers, but they are visibly doing this more than men. The figures for liberal arts colleges are slightly better, with 20.5%. Second, these numbers do not reflect a steady state, as full professors are from a generation where women were less numerous in graduate programs.
But there is still no doubt that the ranks of women are thinning faster than for men throughout careers. Why? I doubt expectations are higher for women, but it is true that many have ambitions more tilted towards family than men. For example, a female graduate student once volunteered to me that her career goal was to teach for a few years, then take care of her family. You would not hear that from a male student.
There may also be some truth to the Larry Summers conjecture: men and women have the same mean ability, but the variance is larger for men. Thus there is a larger proportion of them as you move to the top (or the bottom). This would certainly be consistent with the data, but this does not necessarily prove the conjecture.
Finally, many departments are under a lot of pressure to hire women. The average quality of a female hire has to be lower under such circumstances, and it should not surprise fewer reach tenure and promotion.