Researchers have stated that when it comes to personality or intelligence development then there is not much difference between first-borns and later-borns. First-borns have higher IQ levels and different personality traits that are statistically significant, but practically they are meaningless.

The researchers have studied 377,000 high school students. It is the biggest study carried out on the subject if birth order, IQ and personality. Study’s lead author Brent Roberts from the University of Illinois said that after observing such a large sample, they found first-borns to have higher IQs and different personality traits than the ones born later in the family chronology.

Prof. Rodica Damian at the University of Houston said that statistically the difference is significant, but practically it is not. The research has also found consistent differences in personality traits between the two.

It was found that the first-borns are more extrovert, adjusting and lesser anxious than later-borns. Roberts said that these differences are quite small. “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”, said Damian.

The first-born has single-point advantage in terms of IQ and certain measured personality differences in comparison to those who are born later. Roberts said that the difference is not much and is not noticeable by anyone.

In the study, many factors have controlled that can influence the results, including family size, parental socioeconomic status, family structure, age and gender.