If you think your parents let your younger siblings get away with everything, you're probably right. A study from researchers at Duke, the Johns Hopkins University, and the University of Maryland concludes that parents punish older children more harshly—and that they're wise to do so.
The researchers, who published their findings in the Economics Journal, began by constructing a model of parent-teenager interactions using the logic and mathematical tools of game theory. The model assumes that parents want their adolescent children to avoid long-term negative consequences that can result from risk-taking behaviors such as drinking, drug use, sexual activity, and dropping out of school. Teenagers, on the other hand, are assumed to value the short-term thrills of risk-taking behavior while also wanting to avoid punishment.
The authors posit in the model that parents need a reputation among their children for following through on threatened punishments. This reputation can change if parents do not punish their children after promising they will. This reputation factor proved pivotal, as its predictions varied by the birth order of the children.
According to the authors' theory, parents have an incentive to punish their first-born child if that child engages in risky behaviors in order to deter such behavior by younger siblings. First-born children, recognizing that their parents are likely to be tougher on their transgressions, are generally deterred from being rebellious. However, this deterrence motive for parents is predicted to wane as their younger children reach adolescence.
To test their model, the researchers looked for evidence of differential treatment of adolescent risk-taking by birth order in survey data from the National Longitudinal Study of Youth (NLSY), provided by the U.S. Bureau of Labor Statistics. They found two measures of adolescent rebellion and two measures of parental punishment. Dropping out of high school and getting pregnant were interpreted as rebellion; not allowing a teenager to live in the family house and not financially supporting a teenager were interpreted as punishment.
The results of the researchers' analysis of the NLSY data were consistent with their model. The analysis showed that first-born children who dropped out of high school or got pregnant were less likely to be living at home or receiving financial support from parents than younger siblings in the same situations. Moreover, as predicted, younger siblings were more likely to engage in these behaviors, especially dropping out of school, than their older siblings.