Confirmation this week that Roger Ailes has departed from his perch as CEO of 21st Century Fox's (FOXA) - Get Fox Corporation Class A Report Fox News and Fox Business Network Channel over accusations of sexual harassment and news Biogen's (BIIB) - Get Biogen Inc. ReportCEO George Scangos has stepped down highlights an active year for CEOs changing or leaving positions.

While Ailes, 76, isn't head of the entire media company, his leaving does highlight the pressure public companies are under to remove top-ranking and C-suite executives when that person suddenly becomes a liability. 

In total, the number of CEO departures (including announced departures) from U.S. companies and government or non­profit organizations rose 6% to 624 through the first half of 2016, compared to the first six months of 2015, according to a report out by Challenger Gray & Christmas, a Chicago-based executive outplacement firm.

"The No. 1 reason that CEOs leave is company performance. There's a very clear scorecard," said John Challenger, CEO of Challenger Gray & Christmas in a phone interview. "When earnings and stock prices are down, the executive team can try to explain how external business conditions or other uncontrollable factors lead to the decline. However, when the problems persist, shareholders or the board are more likely to conclude that the issues are not incidental. If the problems are perceived as long-term or as not being addressed, the CEO is typically held accountable."

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Poor performance isn't the only reason why CEOs depart. The majority of exiting CEOs this year gave "resigned" or "retired" as their official reasons for departure, according to the report. Sixty-eight executives left to take positions with other companies and 19 of those as chief executive, while 25 CEOs were ousted from their positions, among other reasons, the report said.

In addition, nine company CEOs have been removed over company bankruptcy or financial losses or due to a scandal. To be fair, not all of the CEOs on this list are leaving on a bad note.

The below list includes CEOs who have exited or announced their exits at public companies in 2016 with market caps of approximately $10 billion or more. (Of note, some CEOs on this list have become chairman.)