If the eldest child in your family is always proclaiming that they know best, then there may a good reason why.
Researchers have discovered that the self-promoting intelligence of first-borns is not all ego: it's scientific fact, as new findings suggest that the eldest child in a family may be smarter than all of their siblings.
In the study, jointly undertaken by the University of Sydney and University of Edinburgh, the data of 5,000 US-based children, collected every two years from pre-birth to age 14, was analysed and assessed.
The researchers looked at the children's performance in tests measuring their reading recognition (to determine their ability to match letters, name names and read single words aloud) and picture vocabulary. Information was also collected on environmental factors such as family background and economic conditions.
The findings, published this month in the Journal of Human Resources, reveal that the eldest child typically scored higher on tests.
"As early as age one, latter-born children score lower on cognitive assessments than their siblings, and the birth order gap in cognitive assessment increases until the time of school entry and remains statistically significant thereafter," the study reads.
"As early as age one, latter-born children score lower on cognitive assessments than their siblings..."
First-born smarts: Nature or nurture?
The researchers reasoned that parental behaviour was a possible cause, suggesting that the firstborns studied usually experienced more mental stimulation from their parents at an early age. And that led to increased intelligence.
While all children got the same amount of emotional support from their parents, the firstborn child got more assistance with tasks related to expanding their analytical skills.
The study also showed that with each new child, the parents' level of participation tended to decrease.
"Our findings suggest that broad shifts in parental behavior from first to latter-born children is a plausible explanation for the observed birth order differences in education and labor market outcomes," the study reads.
But for younger siblings all hope is not lost.
Previous studies have detailed how middle children have tendencies to be family peacekeepers, while the youngest child is typically more create and social than his older siblings, while the position of favourite child is also up for grabs, despite what your parents may tell you.