"RUMORS OF THE death of the old boy network may be exaggerated. Three finance professors at the University of Michigan examined insider trading records for public companies over a 30-year period to see how women executives compared to men. Although all executives tended to profit when buying their own company's stock, men did better on average than women in the same position. This difference was not explained by greater confidence, risk-taking, or opportunism on the part of men. Instead, the data suggest that it's because men seem to have better access to inside information - a leg up on networking with the other (mostly male) executives.
Bharath, S. et al., "Are Women Executives Disadvantaged?" University of Michigan (September 2008)."