Income Mobility, Inequality and Social Welfare

It is often argued that an observation of rising annual income inequality need not have negative normative implications. The argument is that if there has been a sufficiently large simultaneous increase in mobility, the inequality of income measured over a longer time period can be lower despite the rise in annual inequality. In this paper, it is shown by example that if normative implications are drawn from a standard social welfare function, the set of circumstances put forward in the above argument are not sufficient to guarantee that social welfare will improve. The reason is that even though rising mobility does reduce longer term inequality, it also increases the variability of income profiles over time and the latter has a detrimental social welfare effect. Hence, there are two types of mobility: one which reduces inequality (regression to the mean), but another that increases inequality (relative movements uncorrelated with incomes). Further, if individuals' aversion to income variabiltiy is sufficiently larger than the social welfare judge's aversion to inequality, then an increase in mobility, no matter how large, cannot offset the negative normative effect of rising annual inequality