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Birth Order Doesn't Shape Personality?

Photograph by Twenty20

The firstborn natural leader. The rebellious baby of the family. The manipulative, pouty middle child. For centuries, birth order has been said to shape personality.

But several studies, including one polling thousands of adolescent kids, has found birth order and no effect on key personality traits, and that basically everyone thinks they're the family rebel.

The Atlantic's Julie Beck rounded up several of the studies, including one published this week in the Proceedings of the National Academy of Sciences. In the study, researchers in Germany from the University of Leipzig and Johannes Gutenberg University of Mainz, compared siblings within the same family and people with the same birth order across families. What makes their birth order research significant is their sample size—more than 20,000 adults from the United States, United Kingdom and Germany.

Considering the traits of openness, agreeableness, neuroticism, conscientiousness and extraversion, they found no significant effects of birth order. If the received wisdom held, the studies should have concluded firstborns were higher in key traits such as "conscientiousness, neuroticism and the dominance aspect of extraversion," while their younger siblings would have been higher in "agreeableness and the sociability aspect of extraversion."

An even larger study published in the Journal of Research in Personality in July found no birth order effects among 377,000 U.S. high-school students.

They actually did find firstborns to be a bit more conscientious and dominant and slightly less sociable. But the eldest were also slightly more agreeable and less neurotic, which historically would have been predicted in the younger sets. In any case, the effect size was tiny.

The birth order roles are prevalent in how many see themselves. University of Wisconsin counseling student Stacey Armitage concluded in her graduate thesis that college students believed they fit the birth-order roles, though everyone—oldest, youngest, middle—believe they were the most rebellious. And the most considerate.

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