“The Rise and Fall of General Laws of Capitalism,” D. Acemoglu & J. Robinson (2014)

If there is one general economic law, it is that every economist worth their salt is obligated to put out twenty pages responding to Piketty’s Capital. An essay by Acemoglu and Robinson on this topic, though, is certainly worth reading. They present three particularly compelling arguments. First, in a series of appendices, they follow Debraj Ray, Krusell and Smith and others in trying to clarify exactly what Piketty is trying to say, theoretically. Second, they show that it is basically impossible to find any effect of the famed r-g on top inequality in statistical data. Third, they claim that institutional features are much more relevant to the impact of economic changes on societal outcomes, using South Africa and Sweden as examples. Let’s tackle these in turn.

First, the theory. It has been noted before that Piketty is, despite beginning his career as a very capable economist theorist (hired at MIT at age 22!), very disdainful of the prominence of theory. He, quite correctly, points out that we don’t even have any descriptive data on a huge number of topics of economic interest, inequality being principal among these. And indeed he is correct! But, shades of the Methodenstreit, he then goes on to ignore theory where it is most useful, in helping to understand, and extrapolate from, his wonderful data. It turns out that even in simple growth models, not only is it untrue that r>g necessarily holds, but the endogeneity of r and our standard estimates of the elasticity of substitution between labor and capital do not at all imply that capital-to-income ratios will continue to grow (see Matt Rognlie on this point). Further, Acemoglu and Robinson show that even relatively minor movement between classes is sufficient to keep the capital share from skyrocketing. Do not skip the appendices to A and R’s paper – these are what should have been included in the original Piketty book!

Second, the data. Acemoglu and Robinson point out, and it really is odd, that despite the claims of “fundamental laws of capitalism”, there is no formal statistical investigation of these laws in Piketty’s book. A and R look at data on growth rates, top inequality and the rate of return (either on government bonds, or on a computed economy-wide marginal return on capital), and find that, if anything, as r-g grows, top inequality shrinks. All of the data is post WW2, so there is no Great Depression or World War confounding things. How could this be?

The answer lies in the feedback between inequality and the economy. As inequality grows, political pressures change, the endogenous development and diffusion of technology changes, the relative use of capital and labor change, and so on. These effects, in the long run, dominate any “fundamental law” like r>g, even if such a law were theoretically supported. For instance, Sweden and South Africa have very similar patterns of top 1% inequality over the twentieth century: very high at the start, then falling in mid-century, and rising again recently. But the causes are totally different: in Sweden’s case, labor unrest led to a new political equilibrium with a high-growth welfare state. In South Africa’s case, the “poor white” supporters of Apartheid led to compressed wages at the top despite growing black-white inequality until 1994. So where are we left? The traditional explanations for inequality changes: technology and politics. And even without r>g, these issues are complex and interesting enough – what could be a more interesting economic problem for an American economist than diagnosing the stagnant incomes of Americans over the past 40 years?

August 2014 working paper (No IDEAS version yet). Incidentally, I have a little tracker on my web browser that lets me know when certain pages are updated. Having such a tracker follow Acemoglu’s working papers pages is, frankly, depressing – how does he write so many papers in such a short amount of time?

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