(Gianpaolo Pagni for The Washington Post)

A long-brewing debate in corporate America has centered on whether or not the job of CEO and chairman should be split. Proponents for the idea say it reduces the concentration of power in one individual and frees the CEO to focus on running the business. Meanwhile, detractors say that with more independent boards overall, and with the presence of lead or presiding independent directors, there is less of a need to split the roles and little evidence that doing so leads to better performance.

Now, however, there is evidence that combining the roles at least costs more. GMI Ratings, a corporate governance research and rating firm, released a new report late last week showing that employing a combined CEO/chair runs the company about 50 percent more than employing two people. The report finds that executives who hold the jobs of both CEO and chair earn a median total summary compensation of slightly more than $16 million. CEOs without the top job on the board earn a median $9.8 million; a separate CEO and chairman earn a median combined $11 million.

The report also finds that splitting the jobs could positively affect company performance. Corporations that combined the roles are 86 percent more likely to register as “aggressive” in GMI’s Accounting and Governance Risk model. And five-year shareholder returns are nearly 28 percent higher at companies with a separate CEO and chair, the report found.

Despite these numbers, it’s interesting to remember that a majority of U.S. corporations still do not split the roles. According to executive search firm Spencer Stuart’s 2011 board index, only 41 percent of S&P 500 companies separate the job of chairman and CEO, though that number is up from 26 percent in 2001. And perhaps more revealing: Only 21 percent of board chairs are classified as being “independent.”

But back to that cost differential between $16 million for a joint CEO-chairman and $9.8 million for a solo CEO — even accounting for the fact that the average chairman might make more than the average board member (the total average annual compensation for a director in 2011 was $232,142), the discrepancy GMI found is eye-popping. Sure, many CEOs who hold both jobs have undoubtedly been in the job longer, and quite possibly performed better, than those who don’t hold the chairman’s title. The chairman’s job is often retained by a retiring CEO, and then handed down to his or her successor after a few years spent in the new job. As a result, they’re likely to be paid more.

But $6 million more? The average difference seems excessive—perhaps enough so to raise questions from corporate boards who haven’t yet split the role.

Yet to me, it doesn’t seem like boards should need academic studies or research reports to see the downside of combining the two jobs. Putting that much power in the hands of one person has the potential to look like a real conflict of interest, even if lead or independent presiding directors are now the rule and even if it is the entire board’s job to monitor the performance of the CEO. Plus, don’t CEOs have enough to do—and aren’t they paid enough as it is—without giving them even more power and money?

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