If you’re the eldest child in your family, you’ve probably always believed you were smarter than your siblings. Now science is finally backing you up.

Researchers, publishing their work in the journal Proceedings of the National Academy of Sciences, have found that firstborns really are likely to be more intelligent than their siblings.

The researchers analysed data from 20,000 people from three nations, making it the largest and most comprehensive study of its type to date.

However, before you go applying for Mensa membership, you might want to read on. Yes, older siblings are smarter — but only by a single IQ point.

The difference is statistically significant, according to the researchers, but ultimately meaningless in real life.

Beyond intelligence, the study found that birth order had no effect on five key personality traits — extroversion, emotional stability, agreeableness, conscientiousness and imagination.

The study rejects US academic Professor Frank Sullaway’s Family Niche Theory, entrenched since 1996, which claimed that firstborns are more likely to exhibit dominant personality traits because of their physical superiority to their siblings at a young age.

Co-author Julia Rohrer, from the University of Leipzig, told ABC News that she believes the slightly higher IQs displayed by older siblings are more likely a result of social effects, rather than a true sign of biological superiority.

“One theory is that later children ‘dilute’ the resources of the parents, including the attention,” she said.

“The effect does not imply that every firstborn is slightly more intelligent than his or her younger siblings. It means that if you assess the intelligence of a large number of sibships, you will find more sibships in which the firstborn is smarter than sibships in which the laterborn is smarter.

“So as a thirdborn, you could very well be more intelligent than your older siblings, and birth order is only one of multiple factors that can contribute to differences in intelligence amongst siblings.”

Whatever, Rohrer! However you might like to slice it, the study clearly states that firstborns are more intelligent than their siblings — and this firstborn is taking that to the bank.

Is the firstborn child in your group of siblings the smartest? Try your best to argue with scientific fact in the comments below!