Study: Birth order has minimal effects on personality

The findings subvert a variety of tropes about firstborns, middle children and younger siblings.

By Brooks Hays

MAINZ, Germany, Oct. 19 (UPI) -- A survey of more than 20,000 adults from Germany, the United States and Great Britain suggests birth order has only marginal effects on a person's disposition and intelligence.

In analyzing the survey data, psychologists from the universities of Mainz and Leipzig found no correlation between birth order and personality traits like extroversion, emotional stability, agreeableness and conscientiousness.


Researchers did find a small link between birth order and self-reported intelligence levels. First-born adults tended to claim a richer vocabulary and a more natural ability to absorb abstract ideas. Researchers say these claims are backed by the results from more objective studies, which tested sibling intelligence levels. Still, they say, the correlation is minimal.

"This effect on intelligence replicates very well in large samples, but it is barely meaningful on the individual level, because it is extremely small," Stefan Schmukle, a psychologist at Leipzig, in Germany, said in a press release. "And even though mean scores on intelligence decline, in four out of ten cases the later-born is still smarter than his or her older sibling."

The new research, which was published this week in the journal PNAS, subverts tropes about firstborns becoming perfectionists, middle children being peace-makers or younger siblings becoming rebels.


"The real news of our study is that we found no substantial effects of birth order on any of the personality dimensions we examined," Schmukle added. "This does not only contradict prominent psychological theories, but also goes against the intuition of many people."

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