Higher levels of self-confidence translate into a higher income, according to a new study that suggests positive self-esteem offers a big payoff.

The analysis of about 7,000 people found that those with high opinions of themselves as young people earned more in middle age than those with less confidence.

And lead author Timothy Judge, a management professor at the University of Florida in Gainesville, says the widest gap was among those from privileged upbringing.

Those from disadvantaged backgrounds who had a positive self-concept did earn more than their economic peers who lacked self-confidence, Judge says, but the difference was relatively small.

Among those who grew up with more highly educated and wealthier parents, however, the ones with a higher level of confidence earned "dramatically more" than those of the same background with less confidence.

"Our results suggest people who really benefit are the people who have the advantages to begin with," he says. "If you're born with real disadvantages, you're much less likely to have the opportunities."

The analysis, to be published in September in the Journal of Applied Psychology, reviewed attitudinal data between 1979 and 1993 from the National Longitudinal Survey of Youth, a nationally representative sample of people ages 14 to 22.

The researchers then compared earnings in 2002 when the participants were ages 37 to 45. The study controlled for race and gender and evaluated variables such as parents' education and occupation, as well as the participants' education, test scores and poverty status.

Although he says self-esteem is the single best indicator of positive self-concept, Judge says positive self-concept is broader and includes confidence in the ability to perform.

The word "self-esteem" generates a variety of feelings, particularly among those who study behavior. Some, including Jean Twenge, an associate professor of psychology at San Diego State University, have found that unwarranted praise breeds narcissistic children, a subject she has studied at length.

This analysis, she says, "suggests that some level of self-confidence may be beneficial. However, it's important that that not cross over into narcissism, because when it does, that leads to less success."