An MIT economist studied how birth order affects whether a child, particularly a boy, exhibits "delinquency behavior," compared to first-borns in the same family. Joseph Doyle and his colleagues defined delinquency in terms of "disciplinary actions and truancy at school, juvenile delinquency, and adult crime and imprisonment."
The researchers looked at sets of data involving tens of thousands of brothers in two different settings: Denmark and Florida.
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"In families with two or more children, second-born boys are on the order of 20 to 40 percent more likely to be disciplined in school and enter the criminal justice system compared to first-born boys even when we compare siblings," the study reads.
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Doyle told NPR this may be caused by a number of factors, including the second child's need to compete for attention, and the presence of such a young role model in the second-born child's life.
"The first-born has role models, who are adults. And the second, later-born children have role models who are slightly irrational 2-year-olds, you know, their older siblings," he said.
The study mainly focused on differences in second-born boys and their siblings, and found a less significant difference among girls and their siblings.
A separate study earlier this year found that the extra attention first-born siblings receive could lead to a higher IQ.