Temporal evolution of the “thermal” and “superthermal”\nincome classes in the USA during 1983–2001

Abstract

\n \nPersonal income distribution in the USA has a well-defined\ntwo-class structure. The majority of population (97–99%)\nbelongs to the lower class characterized by the exponential\nBoltzmann-Gibbs (“thermal”) distribution, whereas the upper\nclass (1–3% of the population) has a Pareto power law\n(“superthermal”) distribution. By analyzing income data for\n1983–2001, we show that the “thermal” part is stationary in\ntime, save for a gradual increase of the effective temperature,\nwhereas the “superthermal” tail swells and shrinks following\nthe stock market. We discuss the concept of equilibrium\ninequality in a society, based on the principle of maximal\nentropy, and quantitatively show that it applies to the majority\nof population.\n\n