The oldest child receives “more mental stimulation from their parents in the early years,” the study’s authors concluded.
Researchers analyzed statistics from an investigation by the U.S. Bureau of Labor Statistics, the U.S. Children of the National Longitudinal Survey of Youth, which followed 5,000 children from before birth to 14 years old.
Every child was tested every two years on reading recognition and picture vocabulary assessments. Scientists also collected information on family background and economic conditions.
“First-born children scored higher than their younger siblings on IQ tests as early as age 1,” scientists said.
“Although all children received the same levels of emotional support (from their parents),” researchers found that “first-born children received more support with tasks that developed thinking skills.”
Researchers also reported that parental behavior changed as they had more children. They did not offer the same mental stimulation to the younger siblings and engaged less with the younger children in activities like reading, crafts, and even musical instruments, the study found
The report could help explain the so-called birth order effect. Past studies have found that the oldest sibling tends to be better educated and to make more money later in life.
“Our results suggest that broad shifts in parental behavior are a plausible explanation for the observed birth order difference in education and labor market outcomes,” the University of Edinburgh’s Ana Nuevo-Chiquero said.
The study was published in the Journal of Human Resources.