Mr. Piketty hypothesized that income inequality has risen because returns on capital—such as profits, interest and rent that are more gleanings of the rich than the poor—outpaced economic growth. The evidence modern capitalism foments inequality, the former adviser to French Socialist Party candidate Ségolène Royal argued, was in capital’s rising share of income at the expense of labor’s contribution over the last four decades.
But Mr. Piketty’s thesis, posed by the French economist in his controversial 2013 tome “Capital in the Twenty-First Century,” isn’t proved by historical data, says International Monetary Fund economist Carlos Góes.“There is little more than some apparent correlations the reader can eyeball in charts,” Mr. Góes says in a new paper published by the IMF. “While rich in data, the book provides no formal empirical testing for its theoretical causal chain.” Mr. Góes tested the thesis against three decades of data from 19 advanced economies. “I find no empirical evidence that dynamics move in the way Piketty suggests.”
In fact, for three-quarters of the countries he studied, inequality actually fell when capital returns accelerated faster than output.
Those findings support previous work by Daron Acemoglu of the Massachusetts Institute of Technology and political scientist James Robinson, now of the University of Chicago, suggesting Mr. Piketty’s thesis was far too simplistic for the complexities of real-world economies that are affected by politics and technology.