We quantify the contribution of the largest firms to South Korea's economic performance over the period 1972-2011. Using firm-level historical data, we document a novel fact: firm concentration rose substantially during the growth miracle period. To understand whether rising concentration contributed positively or negatively to South Korean real income, we build a quantitative heterogeneous firm small open economy model. Our framework accommodates a variety of potential causes and consequences of changing firm concentration: productivity, distortions, selection into exporting, scale economies, and oligopolistic and oligopsonistic market power in domestic goods and labor markets. The model is implemented directly on the firm-level data and inverted to recover the drivers of concentration. We find that most of the differential performance of the top firms is attributable to higher productivity growth rather than differential distortions. Exceptional performance of the top 3 firms within each sector relative to the average firms contributed 15% to the 2011 real GDP and 4% to the net present value of welfare over the period 1972-2011. Thus, the largest Korean firms were superstars rather than supervillains.

That is from a new NBER working paper by Jaedo Choi, Andrei A. Levchenko, Dimitrije Ruzic, and Younghun Shim.