For those who believe that birth order influences traits like personality and intelligence, a study of 377,000 high school students offers some good news: Yes, the study found, first-borns do have higher IQs and consistently different personality traits than those born later in the family chronology. However, researchers say, the differences between first-borns and "later-borns" are so small that they have no practical relevance to people's lives. The analysis is reported] in the Journal of Research in Personality.

The analysis found -- as a previous large-scale study did -- that first-borns enjoy a one-IQ-point advantage over later-borns, Damian said. The difference is statistically significant but meaningless, she said. The analysis also revealed consistent differences in personality traits between first-borns and later-borns -- first-borns tended to be more extroverted, agreeable and conscientious, and had less anxiety than later-borns, for example -- but those differences were "infinitesimally small," amounting to a correlation of 0.02, Roberts said.

The findings confirmed those seen in the larger study, with specific differences between the oldest and a second child, and between second and third children. But the magnitude of the differences was, again, "minuscule," Roberts said.

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