Gender gaps in earnings

This paper documents and studies the gender gap in performance among associate lawyers in the United States. Unlike most high-skilled professions, the legal profession has widely-used objective methods to measure and reward lawyers’ productivity: the number of hours billed to clients and the amount of new-client revenue generated. We find clear evidence of a gender gap in annual performance with respect to both measures. Male lawyers bill ten-percent more hours and bring in more than double the new-client revenue. We show that the differential impact across genders in the presence of young children and the differences in aspirations to become a law-firm partner account for a large part of the difference in performance.

That is from the new paper "Gender Gaps in Performance: Evidence from Young Lawyers" by Azmat and Ferrer (March 2012). 
A graph from the paper: