Now, after a computer analysis of three decades of hit songs, Dr. DeWall and other psychologists report finding what they were looking for: a statistically significant trend toward narcissism and hostility in popular music. As they hypothesized, the words “I” and “me” appear more frequently along with anger-related words, while there’s been a corresponding decline in “we” and “us” and the expression of positive emotions.

“Late adolescents and college students love themselves more today than ever before,” Dr. DeWall, a psychologist at the University of Kentucky, says. His study covered song lyrics from 1980 to 2007 and controlled for genre to prevent the results from being skewed by the growing popularity of, say, rap and hip-hop.

Defining the personality of a generation with song lyrics may seem a bit of a reach, but Dr. DeWall points to research done by his co-authors that showed people of the same age scoring higher in measures of narcissism on some personality tests.