By Request: Dalton Conley and Sibling Inequality

V asks:

I’d like to know what Matt (and to an extent the commenters on this site) think about Dalton Conley’s work, specifically about how differences between families explain only 25 percent of the nation’s income inequality; the remaining 75 percent is explained by differences between siblings…Thoughts?

This finding would seem to have some negative implications for quite a few preferred policies…

It seems to me that there are some tricky mathematical issues involved in this kind of calculation and I’m not in a position to rigorously evaluate that aspect of Conley’s work. But his findings are certainly interesting. I don’t think they really have the policy consequences they might seem to have at first glance. For one thing, the “only” in “only 25 percent” is doing a lot of rhetorical work — 25 percent is a lot. But more to the point, Conley himself says that socioeconomic status plays an important role in determining the extent of sibling divergence. Here he is writing for the Chronicle of Higher Education in 2004:


Those are among the many stories that illustrate the complicated, rather unpredictable family life of American siblings. We tend to think that brothers and sisters dramatically differ from one another only in extreme cases. The truth is that some families are rafts overcome by stormy seas, some are sailboats tacking through the wind, and some are big, stable ocean liners unconcerned about the weather. In other words, when parents have lots of “class” resources to go around — time, money, social connections — kids often are more alike since parents don’t have to “choose” between them and can actively compensate for disparities in skill or pluck. (Think of the Kennedys or the Bushes.) However, when parental resources are stretched thin because of financial hardship, large family size, short spacing between kids, single parenthood, minority racial status, and so on, kids tend to drift apart in terms of their socioeconomic status. (Think Bill and Roger Clinton.)

Long story short, I think Conley’s work tends to re-enforce the general picture we already have of parental SES being an important determinant of life prospects. But because parents can “invest” disproportionate resources in one child or another — either by design or through quirk of fate — you still don’t see siblings marching in lockstep through the economy.