Consequently, such directors boost a company's stock price on average by about 3 percentage points over a year, said Stephen Ferris, senior associate dean for graduate studies and research at the University of Missouri and co-author of the study.
Investors and others tend to view celebrity directors as a seal of approval, concluding that high-profile figures would not get involved with a bad company, Ferris said.
Celebrities also can help little-known startups, giving them "credibility and visibility much more quickly," Ferris said.
Of course, it doesn't always work out.
Morgans Hotels Group added now-disgraced bicyclist Lance Armstrong to its board when the company went public in 2006. Armstrong resigned in early 2008 after missing every board meeting the year before, even though the company paid him $71,644 in fees and stock awards. He later lost all seven of his Tour de France titles because of a doping scandal.
Why do celebrities join boards? Prestige and a desire to give back or to continue in a leadership role, Fisch said.
And money. Directors can earn six figures for a year's work.
Two years ago, while a graduate student, Chelsea Clinton — daughter of a former president and secretary of state — was appointed to the board of a media and Internet company that gave her $250,000 in restricted stock and a $50,000 annual retainer.
Snowe can expect to earn significantly more on the Price board than the $174,000 salary she received as a senator. Compensation for Price directors last year ranged from $238,823 to $309,618, including stock awards. Snowe has received 4,200 shares of restricted stock.
Price declined to comment beyond statements that Chairman Brian C. Rogers made when announcing the two new directors.
Hrabowski's "focus on helping others succeed fits in well with our mission and our focus on financial education," Rogers said. (Hrabowski also is on the board of Hunt Valley spice maker McCormick Corp.)
And Snowe "has worked extensively on many complex and important issues relevant to our business, including budget and fiscal responsibility, education, retirement and aging, women's issues, health care, foreign affairs, and national security," Rogers said.
Hrabowski was traveling and unavailable, and Snowe could not be reached for comment.
While former politicians are tapped frequently as directors, Maryland companies — some of which cater to the Defense Department — reach out to retired military leaders.
Corporate Office Properties Trust, whose top tenants include Uncle Sam and defense contractors, appointed a retired Navy rear admiral to its board two years ago. One of the directors of TeleCommunication Systems, an Annapolis maker of mobile communications technology used by the military among others, is a retired Marine Corps lieutenant general.
But sometimes a director's experience isn't related directly to the company.
H.C. "Barney" Barnum Jr., a former deputy assistant secretary of the Navy for reserve affairs and decorated former Marine, sits on the board of Medifast, an Owings Mills maker of weight-loss food products. Barnum, 73, said he brings experience in leadership and formulating budgets and policies to the fast-growing company, which is expanding into new markets.
"We have to make timely, accurate decisions, and of course, I've been doing that all my life," he said.
And when Barnum is out representing Medifast, it helps the company when he's introduced as a Medal of Honor recipient. "That makes people listen," he said.
Besides bringing extensive experience running large organizations, Medifast CEO Michael MacDonald said, Barnum has opened doors for the company when it needs to reach out to the military or the government.
"He asks some tough questions," MacDonald added.
Daniel Okrent, the first public editor of The New York Times, will be retiring this month from Tessco Technologies' board after serving for nine years.
CEO Robert B. Barnhill Jr. said in a statement that Okrent brought a "wealth of insight" from his years as a journalist, editor and publishing executive and helped the Hunt Valley company achieve a "laser focus" on its communications.
"Of course, having someone of Dan's stature and renown helped bring attention to Tessco outside of industry circles," he said.
Okrent, 65, said he doesn't consider himself a celebrity director. He contributed to the board by doing the job of a journalist, he said.
"I asked questions like a journalist," Okrent said. Maybe they sometimes would appear self-evident, he said, but "at times they led to new ideas."