The gender gap in the top ranks of corporate America is massive: Women account for just 6% of CEOs at the 500 largest American companies, based on revenue.
But in one sign of change, women were appointed CEO in 12% of transitions to the top job at those companies last year, according to Equilar. That's double the 6% of appointments that went to women in 2018.
The fact that female CEO appointments doubled from 2018 to 2019 sounds like progress. But still, at this rate, it will take more than 40 years to reach CEO gender parity in America.
A total of 78 CEOs announced departures, among those 500 large American companies, according to Equilar.
Of the companies who have announced a successor, 68% were internal promotions, with the remaining 32% being external hires.
Last year, women replaced men in eight of those CEO roles.
Men replaced women who were leaving CEO roles on three occasions.
And most of the time — for 56 CEO roles — men replaced men.
Some evidence also indicates that women who are appointed to the top job aren't necessarily set up for success.
That is a phenomenon researchers have dubbed "The Glass Cliff": high-level women are often promoted at companies during a time of crisis. The appointment of female CEOs traditionally followed poor company performance, according to a 2013 study.
One recent example of this: RiteAid appointed a woman, Heyward Donigan, as CEO to lead restructuring efforts in August of last year. In the prior three years, the company's stock had declined by 95%.
Another example: In October 2018, J.C. Penney appointed Jill Soltau to replace Marvin Ellison, who failed to turn around the struggling retailer. In the prior three years before her appointment, the stock had declined 82%.
And women who are CEOs are generally 45% more likely to be fired than their male counterparts, according to a 2018 study.
What's more: When a company is doing poorly, the rate of firing between men and women is equal, with no statistically significant difference. But when a company is doing well, women are fired at a much faster rate.
The theory of those academic researchers is that when a company is struggling, the decision to fire a CEO is obvious. But when a company is succeeding, there's ambiguity about the impact of a CEO's impact, and board members are more likely to decide a female CEO doesn't have the "right leadership qualities."
Like this story? Subscribe to CNBC Make It on YouTube!