Apple, Suri and Shiloh may be household names because their parents are stars, but a new study of millions of babies finds it's not just celebrities who seek out distinctive names for their kids.

Regular folks do, too, driving down the percentages of those who pick popular names.

The large-scale study of trends in baby-naming by psychologists Jean Twenge and W. Keith Campbell is based on an analysis of names on applications for Social Security numbers of 325 million Americans born between 1880 and 2007.

Twenge, an associate professor at San Diego State University, will present the results Saturday at a conference of the Association for Psychological Science in San Francisco. Campbell is at the University of Georgia-Athens.

Twenge says that the trend of giving children less common names started after World War II and that the most dramatic decline in the more common names occurred during the 1990s, followed by this decade.

People today are more interested in standing out rather than fitting in, she says: "Being unique is now popular."

In 1955, 32 percent of boys had one of the year's 10 most popular names, but by 2007, just 9 percent had names on that list. For girls, 22 percent had a top-10 name in 1955 vs. 8 percent in 2007, the study found.

The study accounted for naming trends as the result of immigration, race and ethnicity, and the same pattern held true, Twenge says.

"People wanted to try to fit in the melting pot, and now people want to embrace their diverse heritage, diverse viewpoint and diverse look," says Pamela Redmond Satran, co-author of 10 books on baby names.

Another study, published online this month in Proceedings of the National Academy of Sciences, found the same move toward uniqueness when it looked at 8,000 U.S. names between 1900 and 2004 and 2,570 names during the same period in France.

"If names get too popular, people may not want them anymore," says co-author Jonah Berger, an assistant professor of marketing at the University of Pennsylvania in Philadelphia.

Twenge, co-author with Campbell of the new book The Narcissism Epidemic, suggests there is a connection between an increase in narcissism in society and wanting baby names that are less common.

Such names illustrate the growth of individualism, she says, which could result in more narcissism.

"We know the desire for uniqueness is going up, and we know narcissism is going up. That doesn't mean we can say it's definitely a cause, but the two are clearly related," she says.

Satran says such changes in naming trends don't mean individualism has taken over.

"A value these days is to say you're unique and have your own individual style, but it's hard to buck the trends," Satran says. "Despite everybody saying they want a unique name, that is still why there are so many named Emily, Jacob, Jaden and Isabella."

Twenge and Satran agree that celebrities may have accelerated the trend toward unusual names, which include creative spellings of popular names.

"I think the celebrity culture celebrates the person who is more special than anybody else," Satran says.

"Not only is it acceptable to have an individual name, but it's going to make you a star."