Some stars have long been aware of Hollywood vanity. Beyoncé Knowles, the pop singer and actress, said recently: “It’s scary that you rarely meet celebrities that are normal. They live on their own diva planets.”

Two Los Angeles psychologists have produced the first scientific evidence that many celebrities sincerely believe that they are better than the rest of us. The psychologists’ forthcoming book suggests that many pop culture icons are heading for disaster.

Mark Young and Drew Pinsky used a mathematical formula to measure the traits, including exhibitionism and vanity, that make up narcissism. Psychologists believe that in general men are both bossier than women and show off more. However, in the “celebrity class” women are far more narcissistic than men and up to a third are more manipulative and vain about their appearance than the typical woman in the street, according to the psychologists from the University of Southern California.

Young and Pinsky have had rare access: celebrities queue up to appear on Loveline, Pinsky’s nationally syndicated radio show, where he has been compared to Professor Anthony Clare, the BBC psychiatrist, for his revealing interviewing style.

They asked 200 celebrities who appeared on the programme to fill out a standard questionnaire called the Narcissism Personality Inventory. They were asked how they felt about themselves, including whether they felt they deserved compliments or were embarrassed by them and whether they insisted on being “respected” at all times.

Participants remain anonymous but interviewees featured on Pinsky’s website include Renée Zellweger, Jessica Simpson, Jim Carrey and members of Duran Duran, the British pop band.

“It was people like that — actors, comedians, musicians and reality TV contestants — who emerged as the most narcissistic of all,” said Pinsky. “The fewer real-life skills they had, the louder they tend to be in their attempts to hold on to attention.”

Fictional examples of narcissists are David Brent of The Office and Miss Piggy from The Muppets. Closer to real life, Courtney Love, the exuberant rock star, once described herself as “over-excitable narcissist”.

Pinsky said: “Vanity is only part of it. They crave attention, are over-confident of their abilities, lack empathy and can behave erratically. But they are often admired and well liked, especially on a first meeting, and perform well in public.”

Knowles said she had noticed a “desperate hunger” around her when she first started making films in Hollywood: “I hope I’m past needing it, as I don’t want to feel the void I see in a lot of celebrities — the unhappiness underneath the smile.”

Young said he suspected that many of today’s Hollywood “fast set”, such as Paris Hilton, Britney Spears and Lindsay Lohan, were in danger of stumbling over the line between fun and malady.

“I have spoken with Nicole Richie, Hilton’s on-off best friend, and she is very polite in private. But she has had a troubled past, her adoptive father [Lionel Richie, the pop star] had admitted he was not a very good parent, and now we see it all coming out in the attention-generating headlines about alleged eating disorders,” Young said.

“They are going further and further. One of these Hollywood party girls is going to be dead in five years’ time.

“We are seeing a new type of celebrity who is famous just for being famous, without a foundation of skills, and this puts the pressure on them to perform ever more outrageously to feed their need for attention. Like Britney being photographed without underwear.”

He added: “We have also found striking differences between the celebrities and their jobs — the more real-life skills they have, such as musicians, the less narcissistic they are.

“In Hollywood they may have found a place that rewards their need for attention.”

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