Science that analyzes sibling birth order and life outcomes is almost destined to go viral, and a recent article on the web site SimpleMost.com suggesting that second-born boys are more likely to become criminals was no exception.
The article, titled "Study Finds That Second-Born Children Are More Likely To Be Criminals,” describes new research from a group of economists demonstrating an increased risk of crime and other delinquency for second-born sons relative to first borns (the study did not look at daughters).
While the topic of birth order on life outcomes has been extensively studied, this report claims to be the first to both quantify the relative risk and investigate the potential causes for these differing outcomes.
But the research is not as definitive as the SimpleMost.com headline suggests. The study is a National Bureau of Economic Research Working Paper and, as such, can be considered something of a work in progress; it has not been formally peer-reviewed or published. Described on the NBER website, these working papers:
Are intended to make results of NBER research available to other economists in preliminary form to encourage discussion and suggestions for revision before publication.
That being said, the research is an important addition to the field due to its large dataset and its study of children from two different social and geographic backgrounds (though both from affluent western nations) — those born in Florida and those born in Denmark. The data the researchers were able to obtain for these two populations of children differed significantly, yet an analysis of both revealed similar trends, as discussed in their paper:
Across both of our locations, and across different estimation techniques, we find that second-born boys are substantially more likely to exhibit delinquency problems compared to their older sibling. In particular, involvement with the juvenile justice system is found to be on the order of 30-40 percent higher compared to the mean level of involvement among first-born boys in both Denmark and Florida.
Incarceration by age 21 is also found to be 40 percent higher in Denmark. These effects are particularly strong among more severe violent crimes (36 percent). In Florida, similarly large effects are found for suspensions in school (29 percent) but effects on truancy are much more moderate and heterogeneous.
The authors also suggested that their data ruled out a number of potential explanations for the difference in outcomes between siblings that they documented:
Our data allow us to explore a wide variety of early-life outcomes in order to study potential mechanisms through which birth order effects are occurring. We are able to rule out broad classes of explanations. We find no evidence that second-born children are less healthy, and indeed second born children appear to be healthier at birth and have lower rates of disability in childhood. We also find no evidence that parents invest less in second-born children's education. These children attend no-worse schools and are more likely to attend pre-kindergarten.
In a July 2017 segment on the study, NPR social science correspondent Shankar Vedantam explained the researcher's primary hypotheses about the cause for the different outcomes:
One possible explanation has to do with the effect of parental time and investment. As many other earlier studies have noted, firstborn kids get the undivided attention of their parents, whereas kids born later are often competing for parental time and resources. Another factor that might be different is the peer group for first- and second-born kids is different. Older and younger siblings come from the same family, but they have different peer groups early in life.
During the same segment, study author Joseph Doyle, an MIT economist and member of the National Bureau of Economic Research, added:
The firstborn 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. 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. It's just very difficult to separate those two things because they happen at the same time.
Being a second-born son does not, of course, doom one to a life a crime and debauchery. This study, however, provided evidence of a higher risk for second-born sons and adds a rich dataset to the scientific literature to explore potential causes.
“These new results have important implications for social policy,” the study concluded. “Our findings that birth order appears to influence the likelihood of delinquency among boys, and that differences begin to appear early, suggests potentially fruitful avenues for monitoring and interventions.”