The researchers traced the phenomenon back to what they called the "self-esteem movement" that emerged in the 1980s, asserting that the effort to build self-confidence had gone too far.

As an example, Twenge cited a song commonly sung to the tune of "Frere Jacques" in preschool: "I am special, I am special. Look at me."

"We need to stop endlessly repeating 'You're special' and having children repeat that back," said the study's lead author, Professor Jean Twenge of San Diego State University. "Kids are self-centered enough already."

"Unfortunately, narcissism can also have very negative consequences for society, including the breakdown of close relationships with others," he said.

The study asserts that narcissists "are more likely to have romantic relationships that are short-lived, at risk for infidelity, lack emotional warmth, and to exhibit game-playing, dishonesty, and over-controlling and violent behaviors."

The standardized inventory, known as the NPI, asks for responses to such statements as "If I ruled the world, it would be a better place," "I think I am a special person" and "I can live my life any way I want to."

The researchers describe their study as the largest ever of its type and say students' NPI scores have risen steadily since the current test was introduced in 1982. By 2006, they said, two-thirds of the students had above-average scores, 30 percent more than in 1982.