New research suggests that birth order amongst siblings only marginally affects one's personality.

Researchers from the University of Mainz and Leipzig in Germany found that central personality traits such as extraversion, emotional stability, agreeableness, and conscientiousness are not affected by birth-order position. Only regarding self-reported intellect small effects were found: Firstborns were more likely to report a rich vocabulary and less difficulty understanding abstract ideas.

The question of whether a person's position among siblings has a lasting impact on personality has occupied scientist for more than 100 years. Laypeople as well a scientist share a number of beliefs: Firstborns are supposedly perfectionists, for example, while middle children develop a talent for diplomacy and last-borns are expected to be rebellious.

For the study, researchers collected and analyzed data from more than 20,000 adults from Germany, the United States, and Great Britain.

These self-reports are not completely unfounded as the study confirmed the already known small decline in objectively measured intelligence from first- to last-born

"This effect on intelligence replicates very well in large samples, but it is barely meaningful on the individual level, because it is extremely small. 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," researcher Stefan Schnukle said in a statement. "The real news of our study is that we found no substantial effects of birth order on any of the personality dimensions we examined. This does not only contradict prominent psychological theories, but also goes against the intuition of many people."

The findings are detailed in the journal Proceedings of the National Academy of Sciences of the United States of America.