Thirty years of data reveals that having many children in large families has a negative impact on cognitive development

A study using 30 years of data on the number of children per family and children's cognitive development found that children in large families had worse school grades and cognitive test results than children in small families, and that It has also become clear that the number of years required for receiving a pension will be shorter.

Effects of Siblings on Cognitive and Sociobehavioral Development: Ongoing Debates and New Theoretical Insights - Wei-hsin Yu, Hope Xu Yan, 2023

For decades, research has shown that children from large families perform worse in school and score lower on cognitive tests than children from smaller families.

It is speculated that the reason for this is that parents do not have enough resources to allocate to their children, resulting in a lack of educational costs, time, and energy.

However, some researchers have suggested that the cause may be due to confounding variables such as parenting style and age, so Professor Wei-hsin Yu, a sociodemographer at the University of California, Los Angeles, and Hope Xu Yan , a sociologist at the University of Maryland, conducted a follow-up survey on the children of all 6,283 women registered in the Bureau of Labor Statistics' survey data ``NLSY79.''

Professor Yu and his colleagues, who compiled the results, confirmed the results of previous studies: the larger the family size, the lower the average cognitive score of children.

We also found that later-born siblings had lower scores than earlier-born siblings of the same age. This seems to suggest that having more children increases the burden of time and money, and reduces the resources available.

Additionally, the study found that having more younger siblings led to lower cognitive scores for older siblings. This tendency is said to be smaller for siblings born later. This is because when siblings are born later on, older brothers and sisters lose a lot of attention from their parents, and from the third child onward, there are no resources left to begin with, so their 'share' rarely decreases. I was told that there is no.

Furthermore, the idea that 'only children' are unpopular in the United States is due to the idea that growing up without siblings hinders the development of cognitive abilities and behavior, but Professor Yu et al. It is denied that the development of children is delayed.