First-born children are smarter than their younger siblings, according to new research.
Economists have waded into the age-old debate and concluded that first-borns have a higher IQ test score than their siblings as early as age one according to Daily mail.
Researchers said the findings could be explained by first-born children receiving more mental stimulation and support in developing thinking skills from their parents during their early years.
The study, conducted in partnership with Analysis Group, examined data from Children Statistics.
Almost 5,000 children were observed from pre-birth to 14 years old on their family background and economic conditions.
Every two years they were assessed on skills including reading and picture vocabulary.
The tests included reading recognition, such as matching letters, naming names and reading single words aloud.
Researchers applied statistical methods to the economic data to analyse how parental behaviour such as smoking during pregnancy was related to their child's test score.
It was found that mothers took 'higher risks' during the pregnancy of latter-born children. Parents also offered less mental stimulation to younger siblings and took part in fewer activities such as reading, crafts and playing musical instruments.
The findings showed that advantages enjoyed by first born siblings start from just after birth to three years of age.
Parents changed their behaviour as subsequent children were born.
Dr Ana Nuevo-Chiquero, said: 'Our results suggest that broad shifts in parental behaviour are a plausible explanation for the observed birth order differences in education.'