You know those high-flying CEOs who get free use of the corporate jet, even for personal reasons? We’ve all envied them. But maybe we ought to be doing something else — like dumping their stock.

New York University professor David L. Yermack recently crunched numbers on 237 large companies. He found that companies that give their CEOs free personal jets perform worse on the stock market than those that don’t. It is, he says, a “dramatic, almost shocking” link — and seems to be driven by investors’ disapproval of the perk. As the New York Times reports:

When companies start disclosing that they have extended this perquisite, he said, their shares drop 2 percent, on average. Then they underperform their market benchmarks by more than 4 percent a year, what he called “just an enormous gap.”

Mr. Yermack likened the effect to what might happen when a high school student gets his first car and, intoxicated by the freedom it affords him, stops studying and falls off the honor roll.

He said he believed speculators could profit simply by betting against companies that invite their C.E.O.’s to steer clear of crowded airports. “If you sold short companies that give this perk and bought all other companies, you would really clean up,” Mr. Yermack said.