"[Psychologists] analyzed several decades worth of data from the Narcissism Personality Inventory, a questionnaire administered in psychology surveys that asks participants to choose between two statements like "I try not to be a show-off" and "I will usually show off if I get the chance." They found that narcissism has been growing since the early 1980s, especially among young people.
Nathan DeWall, a psychologist at the University of Kentucky, has come to the same conclusion [after he] analyzed the lyrics of songs on the Billboard Hot 100 Chart from 1980 to 2007 [and] found a statistically significant trend toward narcissism in the music, with the words "I" and "me" gradually replacing "we" and "us.""
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LiveScience, April-2011