The vast majority of America's brightest young scientists and mathematicians have at least one thing in common. They are male.
While national averages appear to suggest that girls have caught up with boys in maths and science, the reality is that they are still finding it hard to compete with their male classmates at the highest levels.
According to Amy Nowell, of the University of Chicago, there are four males for every one female in the top 5 per cent of the maths rankings. In science the disparity is even more marked, with seven boys for every girl in the top 5 per cent.
The gender imbalance in the top 10 per cent is less pronounced but still very significant: boys outnumber girls by 2:1 in maths and 5:1 in science.
Having scrutinised six national surveys conducted between 1965 and 1992 in an exercise very similar to that carried out by her colleague Amy Thoreson (see above left), Nowell has also discovered that the male-female ratios in the highest-achieving groups have remained fairly constant.
There are also more boys in the lowest-achieving groups, but Nowell argues that it is the imbalance at the top of the ability pyramid that should be of most concern to educationists.
"Gender balance in those occupations that require high levels of maths and science won't be achieved unless these trends are changed," she says. "We will need to encourage more excellence (among girls) if we are to see equality. "
* The huge preponderance of male mathematicians was also highlighted by an Australian study conducted by Gilah Leder and Anne South. The La Trobe University researchers, who traced the career paths of seven men who had won medals in the annual Australian Mathematics Competition, reported that males had gained 91 per cent of the medals issued between 1978 and 1993. The competition attracted entries from 460,000 secondary school students in 1995. Only 43 were awarded medals.
* The practice of using average scores to compare countries' performance in maths and science also helps to mask the huge variation in achievement levels within a nation such as the United States. A paper presented by Leonard Bianchi and Gilbert Valverde, of Michigan State University, pointed out that although America ranked below the mean in maths achievement in the recent Third International Maths and Science Study, a group of US school districts which participated in the study as a single unit recorded the same score as Singapore, the highest-ranked country. In the same study the state of Michigan matched the best in the world in earth science.