Well in a 2003 paper, Uri Gneezy, Muriel Niederle, and Aldo Rustichini put forward an explanation for the existing wage gap between men and women. They say it's because women react less to competitive incentives. And since that means men react more to competitive incentives, men have relatively higher wages.
Now a team of economists led by Christina Gunther is saying there is something incomplete about that result. In their latest paper from the Journal of Economic Behavior & Organization entitled "Women can’t jump?—An experiment on competitive attitudes and stereotype threat," it actually and significantly depends on the kind of tasks. Is it male-oriented task? Female-oriented? Or gender-neural? Gneezy et al.'s results were based on a male task. Gunther et al. are now introducing into the experiment a gender-neutral task and a female task. It turned out they were correct:
"For the male task we replicate their results, but for the neutral task women react as strongly to incentives than men and for the female task women react stronger than men."
One implication of their results is the existence of a "stereotype threat explanation." This provides the adjustment to Gneezy et al.'s theories--women react less to competitive incentives only for task that are meant to be for men:
"Women tend not to compete with men in areas where they (rightly or wrongly) think that they will lose anyway – and the same holds for men, although to a lower extent."
That means also, by further implication, that gender wage gap will always exist as long as there really are tasks that are for men and tasks for women--which is one fact of life. For jobs that are fit for male, we should expect male wages to be higher than women wages. For jobs that are fit for female, we should expect male wages to be lower than women wages. For gender-neutral jobs, it's a toss-up between men and women.
This could also explain why in NASCAR, which we can safely say a male-oriented sport, there are only very few women drivers. And for those women drivers, they seem to have lesser success that men drivers. Take Danica Patrick, for example. There's no doubt the competitiveness is there. But she seems to be only making the headlines whenever she has her race crashes.
Well, now we should make serious changes to the often-cited phrase, "It's a man's world out there."