Middle children, rejoice: Birth order doesn't affect your personality or IQ after all

Better find a new go-to argument, siblings: Your birth order doesn't actually mean all that much.

A new study from the University of Illinois found that the effect birth order has on personality traits and intelligence is negligible, at best. Reported in the Journal of Research in Personality, the study notes that first-born children do have an extra IQ point and slightly more extroverted personalities, but that the differences are "infinitesimally small.”

"If a drug saves 10 out of 10,000 lives, small effects can be profound," University of Illinois professor Brent Roberts said. "But in terms of personality traits and how you rate them, a 0.02 correlation doesn't get you anything of note. You are not going to be able to see it with the naked eye. You're not going to be able to sit two people down next to each other and see the differences between them. It's not noticeable."

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The study, which analyzed 377,000 high school students, compared the children across families, different from earlier studies that have used a "within-family” method the researchers say may have skewed results, because they "don't measure the personality of each child individually,” Rodica Damian, a study contributor at the University of Houston, said. And for parents who argue that they can clearly see birth order differences, the researchers had a pretty obvious comeback:

"The oldest child is always older," Roberts said. "People say, 'But my oldest kid is more responsible than my youngest kid.' Yes, and they're also older."

If only Jan Brady's parents had been able to point to this research each week.