Getting Away With It

It's considered a "fact" of sibling relations: the baby of the family always gets away with murder. If the oldest brother had a curfew of 11 p.m. on weekends, his baby sister just has to call if she's staying out all night. But can it be proven that parents are always stricter with their first born?

Researchers from the University of Maryland, Duke University and The Johns Hopkins University say yes, if there are younger siblings in the family, out of concern for the example that is being set for them. Using economic game theory, which is the use of mathematical analysis to determine what kinds of choices people make, the research team looked at more than 11,000 subjects in the National Longitudinal Study of Youth to predict levels of parental discipline. They also discovered that having one additional younger brother or sister can lower the chance that an adolescent will drop out of high school by 3 percentage points. Researchers also found that though parents are much less likely to financially support or put up with a rebellious teen if there are still younger children at home, their resolve weakens as older siblings move out and younger siblings grow up. "As a result, the theory predicts that last-born and only children, knowing that they can get away with much more than their older brothers and sisters, are, on average, more likely to engage in risky behaviors," says University of Maryland economist Ginger Jin, one of three coauthors of the study. NEWSWEEK's Raina Kelley spoke to Gin about the study and the games teens play. Excerpts:

NEWSWEEK: What inspired you to use game theory on the wrangling between parents and their teens?
Ginger Jin: We were most interested in the role parents play in controlling their children's risky behaviors. Currently, the theories are at two extremes, from "parents have every way to make children do whatever they want their children to do" to the theory that parents are helpless in the face of adolescent behaviors. If we think about this dynamically, we're probably actually somewhere in the middle. But many parents become handicapped by their love for their children and signal to them that they will never abandon their children for behavior they don't approve of. As parents, you care about the welfare of your pregnant teenage daughter so you're going to help her out no matter what. You're not going to throw her and the baby out of the house. To a teen that looks like reward not punishment. So if your daughter can predict that you're going to help her, she is less likely to engage in safe behavior. Of course, that's an undesirable equilibrium from a parents' perspective. But if there are lots of children in the house and the children aren't perfectly sure what their parents will do, they are much less likely to engage in behavior that will get them punished.

How does having young brothers and sisters help parents to stay strict?
With lots of children in the house, the parents still love their children but if they see their first born flirting with risky behavior, parents are more likely to think, "If I help them, the other children will have a bad example set for them." So, they may choose to punish their child if the potential benefit is the better behavior of the younger children.

But that resolve doesn't last by the time parents get to the baby of the family, right?
You will have the tendency to punish your older children, but by the time you move down to your youngest children, you basically rush in with your love to fix the problem. The [rate and severity of the] punishment goes down. If you think of a parent's response as either punishment or reward, if you punish, you have to continue to punish [all your children] or you will never be able to make a credible threat. Just as in the criminal system, the most effective system is deterrence.

Does this theory work for other risky behaviors like unprotected sex or smoking and drinking?
We focused on behavior like pregnancy and dropping out of school, not repeated bad behavior that has yet to produce severe consequences. The baby is a fact, so now a parent's only hope for a benefit is punishment for the sake of the younger children in the house.