CEOs have always had considerable influence over the decision to sell a company, a reality that several recent situations have underscored. Peter McCausland, the founder of Airgas Inc. and a 9.2% shareholder in the company, led a board that successfully opposed a hostile bid from Air Products and Chemicals Inc. Millard "Mickey" Drexler, the CEO of J.Crew Group Inc., drew criticism for approaching TPG Capital about a potential buyout of the clothing company before getting approval from his own board, but shareholders approved the $3 billion deal on March 1. And Richard Wolford, the 65-year-old CEO of Del Monte Foods Co., favored a sale of the company last year because he stood to receive $24 million if that event occurred before his 2012 retirement. The company's $5.3 billion sale to Kohlberg Kravis Roberts & Co. is pending.

John Coates IV and Reinier Kraakman put an academic gloss on the CEO's role in selling a company in their article "The Link Between the Acquisitions Market and the Market for CEOs," which was recently posted on www.ssrn.com. In a study of CEO turnover at Fortune 500 companies between 1992 and 2004, the two Harvard Law School professors "find that acquisitions and internal CEO turnover are most likely to occur at the same point in a CEO's tenure, roughly five years after her initial appointment."

Boards like to give CEOs about five years to prove themselves, the authors say, but tend to fire younger ones and push older ones to retire if the company has performed somewhat poorly during that time. The CEO of such a company may try to line up a sale rather than face defenestration.

But according to Coates and Kraakman, situations such as Del Monte, where a CEO pushes for a sale before he retires, are the exception rather than the rule. Both total CEO turnover and internal turnover (the replacement of a CEO by a means other than a sale) increase with CEO age until the CEO hits 60, at which point the likelihood of a sale stops rising while the possibility of retiring spikes. In other words, the authors write, "Impending retirement is not among the stronger incentives driving the management of target firms to seek friendly buyers," though the possibility of impending CEO job loss is.

Coates and Kraakman also find that the state of the M&A market has a significant influence on CEO turnover. In hot markets, they write, "deals are almost as important a turnover mechanism as retirement, and far more important than dismissal." But when M&A activity slows down, so do CEO firings and retirements, though the authors don't explore the reasons why.

One group of CEOs enjoys significant insulation from the pressures for turnover. Executives with a stake of 1% or more in their company have a median tenure that's 3 times as long as manager CEOs, Coates and Kraakman find, and the stakeholders are also less likely to retire between the ages of 60 and 65, which is when most other CEOs must hand over the reins. McCausland fits into this template, since he continues to run Airgas, but so too does Drexler, who will retain $100 million of equity in J.Crew and continue to run the company after its sale to TPG and Leonard Green & Partners LP closes.

Steven Kaplan of the University of Chicago Booth School of Business and Bernadette Minton of Ohio State University have a ready answer for the question posed by the title of their paper "How Has CEO Turnover Changed?" It's increased, they find. From 1992 to 1999, total CEO turnover averaged 12.6% for an average CEO tenure of just under eight years. Between 2000 and 2007, turnover increased to 16.8%, implying an average CEO tenure of six years. To put it another way, average CEO tenure fell by almost 25% from one period to the next.

The authors find that board-driven turnover has become more sensitive over time to a company's performance relative to its industry, the industry's performance relative to the broader market and the performance of the stock market as a whole. By responding to poor industry and market performance, Kaplan and Minton write, "[b]oards (perhaps in concert with shareholders) perform both the role they performed in the 1980s and some of the role that hostile takeovers played then." Activist investors may cheer that result, but Kaplan and Minton offer a more ambivalent response: "Finally, shorter CEO tenures, the greater sensitivity to stock performance, as well as higher CEO pay may have created a greater incentive for CEOs to engage in earnings management or manipulation." Kaplan and Minton don't explore whether that outcome has occurred, but by raising the possibility, they suggest the risk that CEOs may be tempted to do worse things than try to sell a company if the pressure to achieve results becomes too great.

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David Marcus is senior writer for Corporate Control Alert.