Turnover in the upper echelons of large companies has increased since the Sarbanes-Oxley legislation became law in 2002. One survey of Fortune 1000 companies found a 126% increase in CEO departures from 2000 to 2005. Though executives don't always offer reasons for their departure, some cite increased time spent dealing with more involved boards of directors. "A CEO's job is much less stable than it was 10 or 20 years ago. ... One explanation is that boards are doing their jobs or they're doing their jobs more than they used to," one finance professor suggests.