Institutional Affiliation: Massachusetts Institute of Technology
|The Surprising Hybrid Pedigree of Measures of Diversity and Economic Concentration|
with , : w26512
Measures of economic concentration, such as the k-firm concentration index and the Hirschman-Herfindahl Index (HHI) are commonly used to ascertain the competitiveness of a product market. Within a Cournot model industry equilibrium, it is known a relationship exists between the HHI and the gap between industry price and marginal cost, but the economic theory foundations and intuition underlying the HHI formula are seemingly arbitrary. Here we document that there are indeed powerful and intuitive theoretical foundations to the HHI, but those foundations emanate from outside economics, namely, ecology, where the HHI is known as Simpson’s Diversity Index. We discuss the origins of the HHI and Simpson’s Diversity Index, summarize other measures of concentration, and link them to common meas...