For many years, people have believed that birth order affects personality in some way. Among the more popular stereotypes is that the firstborn tends to be bossy, the youngest tends to be spoiled and rebellious, and the middle child tends to be a loner. However, a new study found that birth order has no effect at all on personality, according to The Guardian.
The researchers gathered data from more than 20,000 people in the U.S., Great Britain and Germany, comparing the characteristics of siblings within the same families. They also compared the traits of people with similar birth order from different families. The researchers specifically looked at the study participants' IQ, extroversion, agreeableness, imagination, emotional stability and conscientiousness.
The study showed that the firstborns had higher IQs than the other siblings. The researchers also found that IQ decreased with decreasing sibling age, meaning the younger siblings tended to score lower on intelligence tests. However, outside of intelligence, the researchers found no other link between personality and birth order.
"This effect on intelligence replicates very well in large samples, but it is barely meaningful on the individual level, because it is extremely small," study author Stefan Schmukle from Leipzig University said in a press release. "And even though mean scores on intelligence decline, in four out of ten cases the later-born is still smarter than his or her older sibling."
The researchers found no association between birth order and personality traits like extraversion, agreeableness, imagination, conscientiousness and emotional stability. Thus, they concluded that "birth order does not have a lasting effect on broad personality traits outside of the intellectual domain."
"This does not only contradict prominent psychological theories, but also goes against the intuition of many people," Schmukle said.
The study was published in the online Oct. 19 issue of the journal Proceedings of the National Academy of Sciences.
