Former chief executives serve on the boards of 38.6% of the top 300 public companies, according to a survey by Boardroom Consultants, New York.
But that represents a decline from past years, according to the survey.
An outgoing CEO's continued involvement on a board may be justified in some cases, for instance if a business is conducting ongoing merger negotiations or the new CEO is recruited from a different industry, according to the survey.
But "it is essential that the new CEO be given the reins if he or she is to be truly effective," said Roger Kenny, partner with the firm that conducted the study.
The trend away from insiders serving on boards and the fact that committees of directors increasingly participate in director selections have resulted in more autonomous boards, the report said.
To many observers, the final step in that process of making a board more autonomous is removal of the former CEO, the report said.