Pareto Coefficient in Income Distribution

Abstract

國家的所得分配呈現明顯雙峰分佈，包含兩個不對稱的柏瑞圖分配。傳統不均度分析不考慮實際的所得分配形式，以整體的單一係數衡量不均度。本研究的目的是考慮國家間所得分佈的實際型態，分析所得不均。考量兩個不對稱的柏瑞圖分配，依所得分佈分組，分別估計柏瑞圖係數以衡量各組的國家群組間的不均度，進而分析不均度與經濟成長的關係。研究顯示兩組國家的不均特質以及與國民所得之關係有顯著的差異，忽略實際組間差異而整體考量可能會造成偏誤結果。

The distribution of income among countries is not symmetrical; rather it is close to Pareto type distribution. It shows consistent bi-modal shape between 1980 and 2007; and shifts to the original Pareto distribution after global financial crisis since 2008. A bi-modal type world income distribution implies a more severe inequality situation between groups of countries rather than among countries. The traditional inequality indexes measured as a whole is an aggregate result. Ignoring the shape of income distributions and difference between groups may overlook some essential features. The purpose of this paper is to investigate the world country income distribution considering its true distribution: bi-modal shape. We suggest to classify countries considering its bi-modal distribution and to estimate the Pareto coefficient of each groups as a complement measure of world income inequality.The result shows that the Pareto coefficient of higher income group is much larger than that of lower income group. Changes of inequality within two groups have significantly different or even opposite directions. The relation between income growth and inequality in the higher income group demonstrates quite different result from the lower income group. And further, the direction of the influences of the mean income on various inequality indexes are opposite between two groups. This study shows that income distributions between two groups possess distinctive features; to measure and discuss the inequality matters as a whole without considering the possible differences between groups may lead to a vague or biased result.