Our general manager wrote a personal check for these tickets and then sold them at a profit.

"This suggests that many managers have sold all that they could," he said.

But if managers do not sell such assets, their cash levels will tend to remain low.

If the company becomes more successful, the managers can again sell the stock publicly.

Enron's senior managers sold large amounts of the company's stock in the months before the company collapsed.

The managers often sell shares after one disappointing earnings report.

Early this year, the managers sold about half of the Amgen shares.

The company went public again in 1986, when the managers sold 46 percent of the stock to the public.

In response, the professors modified their system, so that it now also looks at when a manager buys or sells.

In fact, many managers and directors sell their shares and leave the company.