Oldest sibling is smartest, second-born siblings are troublemakers, studies show (2024)

A new study shows that first-born children tend to be smarter than their siblings and second-born children are more likely to cause trouble.

The University of Edinburgh study reported that the oldest child tends to have a higher IQ and thinking skills than their younger siblings. This is due to higher mental stimulation the first-born receives, CBS affiliate KUTV reports.

The study looked at U.S. Bureau of Labor statistics for 5,000 children from pre-birth to 14-years-old and looks at family background and economic conditions.

"The first-borns scored higher on tests including reading and picture vocabulary, which according to the researchers, could reflect the 'birth order effect,'" Kate Frost said in Country Living magazine. "This means children born earlier in a family go on to have a better level of education and earn higher wages further down the line."

Another study looked at second-born children, who were more likely to misbehave with sometimes 'serious consequences.'

Dr. Joseph Doyle's study found second-born children are 25 to 40 percent more likely to get into "serious" trouble after looking at data from thousands of brothers in the U.S. and Europe.

Parenting styles changing from one child to the next and having siblings as role models are some of the explanations.

"Both the parental investments are different, and the sibling influences probably contribute to these differences we see in the labor market and what we find in delinquency," Doyle told NPR.

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