In an interesting large-sample study led by Michael Ashton and Kibeom Lee, psychology professors from Brock University and the University of Calgary, middle-born children were identified as more cooperative, agreeable, and honest than their older or younger siblings, as well as only children. This study answers an ongoing question in psychology: whether adult personality is related to birth order and the number of siblings in large families.
Study Behind the Findings:
The study was conducted in two phases (Birth order category and larger family size). The first part surveyed over 700,000 participants from Canada, the U.S., Australia, and the U.K, using the six-dimensional HEXACO model- a comprehensive personality questionnaire developed by the researchers 20 years ago.
1. Honesty-Humility (H factor) - Sincerity, Fairness, Greed Avoidance, Modesty
2. Emotionality- Fearfulness, Anxiety, Dependence, Sentimentality
3. Extraversion - Social Self-Esteem, Social Boldness, Sociability, Liveliness
4. Agreeableness (versus anger) - Forgivingness, Gentleness, Flexibility, Patience
5. Conscientiousness - Organization, Diligence, Perfectionism, Prudence
6. Openness to experience - Aesthetic, Appreciation, Inquisitiveness, Creativity, Unconventionality, Altruism
In the agreeableness and honesty-humility dimension, middle children consistently emerged as top scorers by birth order category. These traits show their willingness to cooperate, compromise and avoid manipulating others.
On the other hand, openness to experience traits was higher among the eldest and only children. This was likely due to their more interaction with adults rather than those of their own age
In the second phase, researchers evaluated the impact of family size on adult personality, over 77,000 people were surveyed using the same questionnaire.
The same above traits (cooperative and modest nature) of middle-borns became even more evident in larger families growing up with more siblings.
Not all experts agree with this. Birth order alone cannot determine personality.
To acknowledge this Michael Ashton looked at several factors that could account for the results:
Sibling interactions
Individual personality
Family dynamics
References:
M.C. Ashton, K. Lee, Personality differences between birth order categories and across sibship sizes, Proc. Natl. Acad. Sci. U.S.A.
122 (1) e2416709121,
https://doi.org/10.1073/pnas.2416709121 (2025).
(Input from various sources)
(Rehash/Dr. Disha Merlyn Mathias/MSM)