Glossary
Birth order
A person's position among siblings (oldest, middle, youngest). Large studies find it has little effect on personality.
Birth order is a person's position among their siblings: firstborn, middle child, youngest or only child. Popular books often claim it shapes personality, for example that oldest children are responsible and youngest children are rebels. Large studies don't support that.
A 2015 study in the Proceedings of the National Academy of Sciences used data from about 20,000 people in national panels in the United States, Britain and Germany, and compared siblings both within the same families and across different families (Rohrer, Egloff and Schmukle (opens in a new tab)). It found:
- no birth-order effects on extraversion, emotional stability, agreeableness, conscientiousness or imagination;
- a very small decline, about a tenth of a standard deviation, in self-reported intellect from older to younger siblings, alongside the known small decline in measured intelligence.
The authors concluded that birth order does not have a lasting effect on broad personality traits outside the intellectual domain.
What matters more for siblings is how they are treated. Research links parents' unequal treatment of siblings to less positive sibling relationships (McHale et al. (opens in a new tab)), and the AAP encourages appreciating each child's unique personality. See raising close siblings and parental favoritism.
What you can do today: notice one strength in each of your children that has nothing to do with whether they are oldest or youngest.