*2.2. Gini Coe*ffi*cient*

#### 2.2.1. Concept of Gini Coefficient

The Gini coefficient is an economic statistics indicator that reflects the fairness in general, which is used to reflect whether the distribution of income in social statistics is fair [28,29]. The Lorenz curve is the basis of the Gini coefficient, as shown in Figure 1.

**Figure 1.** Lorenz curve.

On the basis of the Lorenz curve, the Gini coefficient is as follows:

$$G = \frac{S\_A}{S\_A + S\_B} = \frac{2S\_A}{2(S\_A + S\_B)} = \frac{2S\_A}{1} = 1 - 2S\_B\tag{1}$$

The value of the Gini coefficient is equal to twice the value of the area, and is converted to the value of area for the convenience of calculation. It can be found from Equation (1) that, when the area of is zero, the allocation is absolutely fair. The larger the area, the greater the unevenness of the distribution. It is generally believed that, if the Gini coefficient is less than 0.4, it means fairness is basically reached, while if the Gini coefficient is less than 0.3, it means fairness is better.

The calculation methods of Gini coefficient mainly include the direct calculation method, regression curve method, cardinal equal division method, and group decomposition method [19]. Considering the characteristics of the above calculation methods and practical applications, the direct calculation method is applied in this paper, which does not depend on the Lorenz curve. The direct calculation method can ensure that the calculated Gini coefficient value is completely true and accurate without any errors.

#### 2.2.2. Characteristics of the Gini Coefficient

As an index to measure fairness, the Gini coefficient mainly has the following characteristics.

The fairness based on the Gini coefficient does not require all data samples to be identical, but meets certain fairness conditions on the whole, reflecting the overall fairness of samples.


According to the current electricity pricing system in China, the amount of power generation determined by the generation schedule directly determines the operating income of the units. The completing rate of progress of each generator is determined by the power system dispatching. Therefore, it is appropriate to apply the Gini coe fficient to the generation dispatching model in the power system to measure the equilibrium degree of economic income among the generating companies.
