Gini index
It is the most widely cited measure of inequality; it measures the extent to which the distribution within an economy deviates from a perfectly equal distribution.
The index is computed as the ratio of the area between the two curves (Lorenz curve and 45-degree line) to the area beneath the 45-degree line.
Economists use various metrics for measuring income inequality.
Here, the most commonly used measures—the Lorenz curve, the Gini coefficient, decile ratios, the Palma ratio, and the Theil index—are discussed in relation to their benefits and limitations.
The Four criterion of Inequality Measurement Anonymity, Relative Income, Population, and Dalton - YouTube.