First-born children 'smarter than younger siblings'

First-born children are smarter than their younger siblings, according to a new study.

Economists at the University of Edinburgh concluded eldest siblings have a higher IQ test score than their brothers and sisters as early as age one.

Researchers suggested the findings could be explained by first-borns receiving more mental stimulation from their parents during their early years.

The study, published in the Journal of Human Resources, could also help settle the so-called birth order effect when older siblings in a family are said to enjoy better wages and more education in later life.

Almost 5,000 children were observed from pre-birth to 14 years old on their family background and economic conditions with assessments every two years on reading and picture skills as part of the research.