The departing CEOs have left for a variety of reasons. In October alone, we had retirement announcements, voluntary resignations and less-than-voluntary resignations. Hershey's chief John Bilbrey stepped down effective next summer to spend more time with his family. He's been with the company since 2011.
Visa head Charlie Scharf stepped down for personal reasons, effective Dec. 1.
Wells Fargo chairman and CEO John Stumpf stepped down following the revelation that the bank's community banking division had opened up to 2 million accounts for customers without their knowledge.
Caterpillar's Doug Oberhelman will retire in January, after the company's big bet on machinery and equipment didn't pay off. Oberhelman was with the firm for a total of 41 years, including the time before he was chief executive.
The average S&P 500 CEO tenure was around 7.4 years as of 2014, according to a previous Equilar study. That's up from 6.6 years in 2005. The next four years will see a reconfiguration of businesses' relationship to politics, and it's anyone's guess how that will affect CEO tenure.