One's family birth order has no bearing on personality, according to a new study released by the National Academy of Sciences. The study puts to rest armchair psychologists’ theories that younger children are extroverted or agreeable, and that the eldest is and will always be a bossy boots.
However there may be some intellectual effects in birthing order as the study finds that firstborn children tend to score higher on "objective measures of intelligence and self-reported measures of intelligence". Apart from this, other results in the study contradict both scientific and common ideas about how much influence birth order has.
The data for the study was collected from 20,000 participants in the UK, Germany and the U.S. Because of the large sample size, researchers were able to identify "even very small effects of birth order on personality with high statistical power".
The researchers grouped the subjects' birth orders by establishing their position among children in a household - if a child was raised as the eldest or second-born in a family, they were treated as such, rather than taking into account if they did or did not have other siblings who did not live in the home. The researchers decided on this method because birth-order effects are believed to develop from the homes' social environment, rather than actual biological markers.
Once all of the data was collated, the researchers analyzed it to see if personality features or intelligence was related to family size, birth order or country of residence.
As expected, the data showed a strong effect of birth order on intelligence. The theory behind this is that parents have more time and emotional and intellectual resources to dedicate to their first child, boosting the intelligence of the firstborn.
In contrast, the survey showed no significant effects of birth order on the "Big Five” personality traits - emotional stability, extraversion, agreeableness, openness to experience, and, conscientiousness.