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The study is by Christopher F. Chabris and Mark E. Glickman and is entitled "Sex Differences in Intellectual Performance: Analysis of a Large Cohort of Competitive Chess Players." It was published in the latest issue of the journal Psychological Science, which has put an abstract online:
Only 1% of the world's chess grandmasters are women. This underrepresentation is unlikely to be caused by discrimination, because chess ratings objectively reflect competitive results. Using data on the ratings of more than 250,000 tournament players over 13 years, we investigated several potential explanations for the male domination of elite chess. We found that (a) the ratings of men are higher on average than those of women, but no more variable; (b) matched boys and girls improve and drop out at equal rates, but boys begin chess competition in greater numbers and at higher performance levels than girls; and (c) in locales where at least 50% of the new young players are girls, their initial ratings are not lower than those of boys. We conclude that the greater number of men at the highest levels in chess can be explained by the greater number of boys who enter chess at the lowest levels.
For those of you who want to catch the gist without actually procuring the journal, here are some highlights from the summary provided by Chabris and Glickman:
There could be some innate difference in ability between men and women overall with respect to the skill required to play chess well. This difference in average or in variability need not be large; at the upper tail of the distribution where chess players operate for say spatial ability, a small difference would result in a large difference in representation. They call this the ability distribution hypothesis.
Discrimination could result in a difference in participation through different standards. However, they note that this is not a problem for this particular study because Chess rankings are objective measures. You can't discriminate against someone when their gender cannot be calculated into their performance.
There could be a differential drop-out rate between boys and girls. Equal numbers of boys and girls with equal abilities could begin chess training, but fewer girls could see it through to becoming chess grandmasters. They call this the differential dropout hypothesis.
Fewer women could self-select to participate in chess. If fewer talented women choose to participate in chess in the first place, by attrition alone there will be fewer in the resulting grandmaster pool. They call this participation rate hypothesis.
After examining the data Chabris and Glickman come to the following conclusions:
Men and women differed in chess ability in all age groups even after differences like frequency of play (read: level of training) or age were taken into account. The disparity between men and women in ability exists at the beginning and persists across all age groups.
No greater variance is to be found in men than women – if anything in most age groups women had a higher variance than men.
Women and men do not drop out more or less frequently when ability and age are factored out. For example, if you are not very good at chess you are more likely to stop playing tournaments, but girls and boys that are equally good are equally likely to stop playing. This strikes a blow at the differential dropout hypothesis.
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.
There is a mores extensive description in the Science blog "Pure Pedentary", where the subject can also be discussed.
