Eldest siblings are more intelligent, a new study of 377,000 high school students finds. However, the difference is equal to, on average, just one IQ point. This difference is so small as to be almost meaningless.
There were also consistent differences in personality.
Eldest siblings tended to be more outgoing, conscientious and agreeable, while being less anxious. But, again, these differences were very small.
Professor Brent Roberts, who led the study, explained how small the differences were:
“In some cases, if a drug saves 10 out of 10,000 lives, for example, small effects can be profound.
But in terms of personality traits and how you rate them, a 0.02 correlation doesn’t get you anything of note.
You are not going to be able to see it with the naked eye.
You’re not going to be able to sit two people down next to each other and see the differences between them.
It’s not noticeable by anybody.”
The study controlled for factors like economic status and the number of children.
Professor Rodica Damian, who co-authored the study, said:
“The message of this study is that birth order probably should not influence your parenting, because it’s not meaningfully related to your kid’s personality or IQ,”
The research was published in the Journal of Research in Personality (Damian & Roberts, 2015).