Researchers drew from a pool of 140 female CEOs within the largest U.S. publicly traded companies, representing just over 4.6 of the total CEO population, and excluded founders or those who inherited their position from a family business. Of those, they then selected 100 and matched each one with a male CEO from a similar industrial sector and company size for comparability purposes. They then used Bloomberg profiles, press releases, company websites and news articles to track each CEO's career path. 

What they found was that women who become CEOs were much more likely to have served on a public company board than men, 59 percent versus 42 percent. The difference was even more stark with regard to private boards: 23 percent of female CEOs had previous experience on the board of a private company versus 12 percent of men. 

Further, when women were recruited from the outside, they were far less likely to have had previous CEO experience. The researchers found that 52 percent of male CEOs had been the CEO of a private company or a division of a public company before, versus 18 percent of women. Instead of CEO, they were more likely to have served in another C-level or senior executive role. On the other hand, when an insider was recruited, the path was nearly identical: 70 percent had previously served as chief operating officer, showing a clear path from COO to CEO. 

"Together these findings not only illuminate a viable pathway to CEO for aspiring women (through board service) but also offer a suggestion for companies and boards that seek gender diversity in their CEO ascension plans: Assist high-potential executive women in securing corporate board seats," said the researchers. "Our findings suggest that boards of directors should consider the skill set of COO, president, or even executive vice president roles combined with board experience to approximate prior CEO experience. Service on corporate boards may also give women visibility with board members who oversee CEO appointments so that they are more likely to be considered in CEO searches."