Why are there so few women among chess grandmasters? (Of 894 in 2004, eight were women.) Pure Pedantry reports on the results of a study by Chabris and Glickman, and the answer, in a word, is participation. In more than a word:
If you look at the participation rate of women and relate that to performance, you find that in cases where the participation rate of women and men is equal the disparity in ability vanishes. Basically, this means that in zip codes where there are equal numbers of men and women players there is no great disparity between male and female ability - and certainly not a disparity in ability large enough to explain the difference in the numbers of grandmasters.(Via Yet Another Sheep.)