First-born children tend to be more intelligent than their siblings, perhaps because they get extra parental attention in early life compared to siblings, a new study finds.

Researchers examined data from 5,000 children who completed reading and picture vocabulary tests every two years until age 14 and found that first-borns had higher IQ test scores beginning as young as one year old, The Independent reported.

The differences in test scores between first-borns and other children increased with age, according to the study in the Journal of Human Resources.

While all children in the study received the same level of emotional support from parents, first-born youngsters were given more parental support with tasks that involved thinking, The Independent reported.