In larger analyses, the link between birth order and personality traits appears much weaker. A 2015 study looking at more than 20,000 people in Germany, the United Kingdom and the United States found no link between birth order and personality characteristics – though the researchers did find evidence that older children have a slight advantage in IQ. (So, eldest daughters, take your bragging rights where you can get them.)

Damian worked on a different large-scale study, also published in 2015, that included more than 370,000 high schoolers in the United States. It found slight differences in personality and intelligence, but the differences were so small, she says, that they were essentially meaningless. Damian did allow that cultural practices such as property or business inheritance (which may go to the first born) might affect how birth order influences family dynamics and sibling roles.

Still, there is no convincing some siblings who insist their birth order has predestined their role in the family.

After her study published, Damian appeared on a call-in radio show. The lines flooded with listeners who were delighted to tell her how skewed her findings were.

“Somebody would say: ‘You’re wrong! I’m a firstborn and I’m more conscientious than my siblings!’ And then someone else would call in and say, ’You’re wrong, I’m a later-born and I’m more conscientious than my siblings!” she says.

What personal experience says

Sara Stanizai, a licensed marriage and family therapist in Long Beach, California, runs a virtual group with weekly meet-ups, where participants reflect on how they believe their birth order has affected them and how it may be continuing to shape their romantic lives, friendships and careers.

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The program was inspired by Stanizai’s experience as an eldest daughter in an Afghan-American family, where she felt “parentified” and “overly responsible” for her siblings – in part because she was older, and in part because she was a girl.

While Stanizai acknowledges that the research around birth order is mixed, she finds it useful for many of her clients to reflect on their birth order and how they believe it shaped their family life – particularly if they felt hemmed in or saddled by certain expectations.

Her therapy groups spend time reflecting on questions like: How does my family see me? How do I see myself? Can we talk about any discrepancies in our viewpoints, and how they shape family dynamics? For instance, an older sibling might point out that he or she is often the one to plan family holidays. A younger sibling might point out that he or she often feels pressured into going along with whatever the rest of the group wants.

Whether or not there is evidence that birth order determines personality traits is almost beside the point, experts acknowledge.

“I think people are just looking for meaning and self-understanding,” Stanizai says. “Horoscopes, birth order, attachment styles” are just a few examples, she says. “People are just looking for a set of code words and ways of describing their experiences.”

The New York Times

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