Chief executives continue to leave office at a high rate, with many departures stemming from pay issues or board disputes, according to new study by consulting firm Booz Allen Hamilton.

Almost one in three CEOs was forced out of office in 2006--compared with one in eight in 1995--Booz Allen Hamilton reported in its sixth annual Global CEO Succession Study. The survey of the world's 2,500 largest companies showed that corporate boards in the past few years have replaced underperforming CEOs at a quicker rate, though the number of performance-related dismissals actually declined slightly in 2006. There is also an increasing focus on grooming internal candidates in the face of mediocre performance by CEOs recruited from outside the firm.

"It's clearly time to say goodbye to the age of the imperial CEO," Steven Wheeler, senior vice president of Booz Allen Hamilton, said in a May 22 press release on the study, which is subtitled, "The Era of The Inclusive Leader."

Wheeler said inclusiveness is a new critical CEO survival skill--and those top executives who do not give board members a voice in the company's growth strategy are in real danger of being forced out. The number of CEOs who lost their jobs because of conflicts with directors rose from 2 percent in 1995 to 11 percent in 2006.

However, the study does suggest that the wave of performance-related turnover--which grew by 318 percent between 1995 and 2006--may be subsiding. Thirty-two percent of CEOs who left office involuntarily in 2006 were forced out because of performance issues or board infighting--a slight decrease from 2005, the authors write.

In fact, the authors write that overall CEO turnover worldwide peaked in 2005. Study data shows that average CEO tenure is beginning to rise again as well, reaching a worldwide average of 7.8 years in 2006, with the Asia-Pacific region having the highest average retention period, 9.5 years.

The one notable exception was the increased rate of departures due to mergers and acquisitions. In 2006, 22 percent of departing CEOs left because of a merger or buyout, compared with 18 percent in 2005. Europe and North America saw the highest rates of turnover, the study says, because of elevated merger activity in both regions.

Study data continues to indicate that outside CEOs with prior experience as a chief executive of a publicly traded company deliver slightly lower returns to shareholders than internally promoted candidates.

The authors also advocate for the separation of the roles of chairman of the board and CEO, saying those companies with a completely independent chair who had not previously been CEO brought the best returns to investors over the study period. U.S. shareholders continue to press for separation of the two roles, though this proxy season has only seen an average of 28.4 percent support for the proposal at 10 meetings where results are known.