Rawls' Fairness, Income Distribution and Alarming Level of Gini   Coefficient
  The argument that the alarming level of Gini coefficient is 0.4 is very popular, especially in the media industry, all around the world for a long time. Although the 0.4 standard is widely accepted, the derivation of the value lacks rigid theoretical foundations. In fact, to the best of our knowledge, it is not based on any prevalent and convincing economic theories. In this paper, we incorporate Rawls' principle of fair equality of opportunity into Arrow-Debreu's framework of general equilibrium theory with heterogeneous agents, and derive the alarming level of Gini coefficient formally. Our theory reveals that the exponential distribution of income not only satisfies Pareto optimality, but also obeys social fairness in Rawls' sense. Therefore, we specify the maximal value of the Gini coefficient when income follows exponential distribution as a possible alarming level. Our computations show that the alarming level should be specified at least equal or larger than 0.5 rather than 0.4. We empirically investigate if our model receives support from a large data set of all kinds of countries all over the world from Word Bank in 1990, 1995, 2000 and 2005 using the distribution fitting and statistical decision methodology. The results suggest that the value of 0.4 is around the mean of the Gini coefficients, corresponding to the most probable event in a peaceful world, rather than the alarming level, while the two-sigma rule shows that in our sample the alarming levels are all larger than 0.5, conforming to the predictions of our theory. 
Yong Tao, Xiangjun Wu, Changshuai Li
q-fin.GN physics.soc-ph