Social mobility across the generations

The Economist reports on Greg Clark’s work using surnames to track social mobility. I have posted about this work before, but The Economist piece makes an important point. When tracking mobility across generations, you cannot simply extrapolate the results of a single generation into the future.

Corak’s work draws on recent studies that compare income levels between just two generations: fathers and sons. That is out of necessity; good data covering three or more generations are scarce. But reliance on limited data could lead to overestimates of social mobility.

Gregory Clark, an economist at the University of California, Davis, notes that across a single generation some children of rich parents are bound to suffer random episodes of bad luck. Others will choose low-pay jobs for idiosyncratic reasons, like a wish to do charitable work. Such statistical noise makes society look more changeable than it is. Extrapolating the resulting mobility rates across many generations gives a misleadingly sunny view of long-term equality of opportunity. Mr Clark suggests that family history has large effects that persist for much greater spans of time. Fathers matter, but so do grandfathers and great-grandfathers. Indeed, it may take as long as 300-500 years for high- and low-status families to produce descendants with equal chances of being in various parts of the income spectrum.

In line with his earlier work, Clark fingers a genetic basis to the finding.

Mr Clark’s conclusion is that the underlying rate of social mobility is both low and surprisingly constant across countries and eras: the introduction of universal secondary education scarcely affects intergenerational mobility rates in Britain, for example. This consistency, he suggests, shows that low mobility may be down to differences in underlying “social competence”. Such competence is potentially heritable and is reinforced by the human tendency to mate with partners of similar traits and ability.

This work reminds me of an article in which Sam Bowles and Herb Gintis explore the inheritance of inequality. They estimated that intelligence is responsible for a correlation between parent and child income of 0.01, with total correlation due to genetic factors of around 0.12. I played with the results to show that a larger proportion of the observed variation could be explained by genetics if you tweak some of the assumptions. However, Clark’s work shows that a larger limiting factor on their result was a single generation comparison in their analysis.

Postscript: A debate followed the Economist article, with contributions by Miles CorakFransicso FerreiraGreg Clark (and again), and Jason Long. They are all worth reading.

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