Measuring Plutonomy Intensity Under Data Deprivation: An Axiomatic Index

Abstract

Measuring top-income inequality typically requires household surveys merged with tax records, or Pareto tails fitted to survey data, resources unavailable across much of the developing world. In this note, we propose a simple plutonomy intensity index estimable from alternative sources. Three axioms, within-group irrelevance, joint income scaling invariance, and plutocratic income monotonicity, characterize the class of indices ranking distributions exactly as the plutocrat-to-ordinary mean income ratio does. The index also satisfies anonymity, population invariance, and a restricted transfer principle. We illustrate its use in the Arab region, approximating it using the Forbes Billionaires List and World Bank macroeconomic data.