Second-born boys are 40 percent more likely than their siblings to end up in prison, a new study suggests. Researchers examined robust datasets from Denmark and the United States, and ruled out the possibility that these higher rates of delinquency were due second-borns having health problems or attending inferior schools. They did, however, identify one likely cause—firstborns are raised by their parents. Second-borns? Their immature siblings.
“The firstborn has role models, who are adults,” coauthor Joseph Doyle of MIT told NPR. “Second, later-born children have role models who are slightly irrational two-year-olds, you know, their older siblings.”
Psychologists and economists have been studying birth order since at least 1928, when Alfred Adler published a paper in the now-defunct journal Children, claiming that birth order could impact how children develop. More recently, a 2005 study found that later-born children are inferior students, sexually promiscuous, and less successful employees. So Doyle’s new claim that second-borns may also be delinquent convicts is really just icing on the cake.
For the study, submitted to the National Bureau of Economic Research, Doyle and colleagues took advantage of Denmark’s notoriously open data. By combining figures from the Danish Birth Register with the country’s Criminal Register and School Register, they were able to track the criminal and academic record of any child born after 1960. In the U.S., these figures were less easy to come by. Fortunately Florida (yes, Florida) recently merged a large number of the state’s birth records with school records, allowing researchers to track kids born after 1992 through high school. And since one Florida school district now reports whether its students have been incarcerated in juvenile detention centers, the researchers were even able to link American students to the criminal justice system.
After examining the data, Doyle and colleagues found no evidence that second-born children are less healthy or have higher rates of disabilities than their siblings. They don’t attend worse schools and, indeed, they’re more likely than firstborns to attend preschool. What they did find is that second-borns in both countries are 40 percent more likely to be involved with the juvenile justice system and, in Denmark, incarcerated before age 21. Second-borns are also 36 percent more likely to be involved in violent crimes and 29 percent more likely to be suspended from school.
The only datapoint Doyle and his team found that could account for the disparity is that mothers tend to return to work before their second-borns are four years old. Do second-borns act out because, as toddlers, they get less maternal attention? Doyle considers it a distinct possibility, but stresses that more research is necessary.
“Both the parental investments are different, and the sibling influences probably contribute to these differences we see in labor market and what we find in delinquency,” he told NPR. “It’s just very difficult to separate those two things.”