MEDIA RELEASE – January 14, 2025 – R0005
Feeling particularly agreeable and unpretentious? You can give a nod to your siblings for that.
New Brock University co-led research says personality development is influenced by the number of siblings a person has and when they were born in relation to those siblings.
“It does seem that people who grew up with more siblings are, on average, more co-operative and modest,” says Professor of Psychology Michael Ashton, one of the leads on the study.
“We found co-operative characteristics averaged highest in middle-born children followed by youngest child, then oldest child, then children who had no siblings,” he says.
Ashton and Professor of Psychology Kibeom Lee at the University of Calgary studied two groups of online research participants, most of whom were from Canada, United States, Australia and the United Kingdom. The study is one of the largest of its kind on the connections between personality and birth order, a topic that has been debated among researchers for decades.
A group of 700,000 participants were asked to indicate their birth order — first, middle or last born — or if they were an only child. The study described siblings as being children raised in the same household regardless of whether they were biologically related.
The participants were asked to fill out a detailed personality questionnaire — called the HEXACO Personality Inventory — that Ashton and Lee created about 20 years ago.
It measures six major dimensions of personality, with sincerity and modesty being hallmarks of people with high honesty-humility levels. High scorers also avoid manipulating others for personal gain, aren’t tempted to break the rules and aren’t interested in attaining excessive wealth and social status.
One of the other five personality characteristics is agreeableness. Those scoring high in this category more easily forgive, are less judgmental, are more willing to compromise and co-operate with others, and can easily control their temper compared to those with a lower score.
The researchers found that honesty-humility and agreeableness showed the largest differences among birth order categories.
People with siblings older and younger than them scored the highest in these two categories, followed by the youngest and then the oldest siblings. Only children scored the lowest.
“Many people are exceptions to these trends, but the differences in the average levels were clear,” says Ashton.
Ashton and Lee initially wondered if there might be “something special” about people born in the middle of a sibling group, but realized the results might be linked to the number of siblings people grew up with.
To test their theory, the researchers then surveyed members of a second group of 77,000 participants on the number of siblings they grew up with.
They found the more siblings participants had, the higher their levels of honesty-humility and agreeableness, on average.
“The differences are too small to draw conclusions about individuals, but trends in the average levels of these traits were clear,” says Ashton.
Among people with the same number of siblings, middle- and youngest-born averaged slightly higher than the oldest.
Ashton says he and Lee looked at several factors that could account for the results.
“It may be just that you need to compromise and co-operate more when you grow up with siblings,” he says. “Maybe this has a long-run effect on your personality, affecting your general inclination to co-operate.”
But single-child households take heart: Ashton and Lee’s research showed adults who had no siblings scored higher in the HEXACO Personality Inventory’s “Openness to Experience” category — intellectual curiosity and exploration being key features — than people who had siblings.
“If you’re the only kid in the family, your intellectual environment is at a pretty high level and more stimulating because you’re interacting with your parents and other adults,” says Ashton, adding that firstborns also score higher than younger siblings.
For more information or for assistance arranging interviews:
*Sarah Ackles, Communications Specialist, Brock University [email protected] or 289-241-5483
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