In the wake of the Boston marathon bombings, Alix Spiegel reviews research on influential siblings:

Consider, for example, the research that looks at how much a parent who smokes influences his child to smoke, versus the degree to which an older sibling who smokes influences a younger sibling. “Both can tsarnaev-brothers-thumbhave an effect, but in a lot of studies they’ve found that the effect ‘older sibling smoking’ has is greater than the effect that ‘parental smoking’ has,” Rende says. It’s the opposite of what many people assumed, he says. Older siblings are more influential.

Rende says you can see this influence of big brothers and sisters in all kinds of families — rich, middle class and poor. But their power is really magnified in the particular subset of families he studies: families that are psychologically and economically unstable. In those families the power of the older sibling is much greater because parents aren’t around as much, and the siblings tend to spend a lot of time together. …

[T]he reverse is also true. Good behavior in older siblings can be as contagious as bad. It just seems that — particularly when families are struggling — the fate of the kids is more tethered to their siblings than we originally thought. For good and, apparently, for bad.