In this section, to illustrate the method proposed in this paper, we examine two examples in order to provide a ranking for DMUs.
5.1. Example1
Meng et al. [
40] provide a small example, which presents data for six recent road construction projects with three inputs and three outputs, as
Table 2 shows (the data taken from Meng et al. [
40]), where inputs are investment return period, amount of investment, network adaptability, and outputs are network structure, surroundings environmental harmonizing, society needs. Next, we will analyze the efficiency of six recent road construction projects.
After calculating the CCR model, the cross-efficiency matrix is listed in
Table 3.
According to the cross-efficiency matrix, the elements in the diagonal are the CCR efficiency scores of DMUs, which can be seen as a self-evaluation.
Table 3 reports DMU
2, DMU
3, DMU
4 are all efficient DMUs. Thus, in order to further distinguish between these DMUs, we analyze the cross-efficiency matrix by our proposed approach.
Step 1. Normalize the cross-efficiency matrix. We can obtain the normalized matrix as follows.
Step 2. Determine the ideal solution as Formula (7).
Step 3. Construct the grey correlation matrix between DMU and the ideal solution. According to the grey correlation analysis, we can obtain the grey correlation matrix by Formula (8) as follows.
Step 4. Calculate the weights set of criteria. The weight
of the
j-th criteria is calculated by Formula (13) and (14), so we can get the weights set as follows.
Step 5. Calculate the grey correlation degree between the DMU and the ideal solution is as follows.
From the results of the grey correlation degree, is the largest of them, which denotes DMU2 is highly relevant to the ideal solution, is the smallest of them, showing that the correlation between DMU1 and the ideal solution is small.
Step 6. Calculate the relative entropy between DMU and the ideal solution. According to Formula (12), the weighted relative entropy between each DMU and the ideal solution is
From the values of the relative entropy, is the smallest of them, which shows that DMU2 is closer to the ideal solution than other DMUs. is the biggest of them, showing that DMU5 is farther away from the ideal solution than others.
Step 7. Normalize
and
according to Formula (15).
Further, by integrating grey correlation degree with relative entropy by Formula(16),we can get the results as follows.
Through the calculation of grey relative degree and relative entropy, first, it can be found that the effective unit is further distinguished, DMU
2 is the most relevant to the ideal solution, and DMU
3 and DMU
4 are inferior to DMU
2. Then, with the TOPSIS results as shown in
Table 4, it indicates that the efficiency trends based on relative entropy evaluation method and TOPSIS are consistent, but the efficiency change based on relative entropy is more obvious, which is more convincing. Combined with the grey correlation degree, the data similarity analysis can fully reflect the data situation change and geometric similarity. Finally, it can be concluded that all DMUs are ranked as DMU
2 > DMU
3 > DMU
4 > DMU
6 > DMU
5 > DMU
1.
In order to assess the ranking merits of our proposed method, we apply different methods to rank DMUs. All the ranking results are listed in
Table 4.
Table 4 reports that the CCR efficiencies, the rankings provided by the three different models and our proposed method, from which it is seen that there are three efficient DMUs in the CCR efficiency that cannot be further discriminated, where as our proposed approach provides the ranking result of DMUs. And the ranking result is identical to the three methods, the average cross-efficiency, benevolent method, and our proposed method, the ranking is DMU
2 > DMU
3>DMU
4 > DMU
6> DMU
5 > DMU
1.
However, the TOPSIS method by Wu et al. [
26] results in a different ranking for some DMU in the six DMUs, such as the worst DMU is DMU
5 instead of DMU
1. By comparing the results, we find that the closeness results based on relative entropy are the same as TOPSIS, and DMU
1 is closer to the ideal solution than DMU
5. However, by analyzing the grey correlation degree, it is found that the DMU
5 is more related to the ideal solution from the similarity of the sequence curve. Moreover, as shown in
Table 3, the DMU
5 is better than the DMU
1 under various standards. Therefore, with comprehensive information, DMU
5 is preferable to DMU
1.
5.2. Example 2
Shang and Sueyoshi [
41] provide an example, where they describe data for the technology of manufacturing systems with two inputs and four outputs, as
Table 5 shows (the data taken from Shang and Sue Yoshi [
41], Wu et al. [
30]). Inputs are the annual operating and depreciation cost (in units of
$100,000), the floor space requirements of each specific system (in thousands of square feet). Outputs are the improvements in qualitative benefits (%), work in the process reduced (10), the average number of tardy jobs reduced (%) and the average yield increased (100) [
30]. Next, we will analyze the efficiency of these DMUs.
The cross-efficiency matrix is calculated by the CCR model, as shown in
Table 6.
The cross-efficiency matrix shows that the elements in the diagonal are the CCR efficiency scores of DMUs, which can be seen as a self-evaluation.
Table 6 shows DMU
1, DMU
2, DMU
4, DMU
5, DMU
6, DMU
7, DMU
9 are all efficient DMUs. It is impossible to achieve a full ranking for all the DMUs. Thus, in order to get the ranking of all DMUs, we analyze the cross-efficiency matrix by our proposed approach.
Step 1. Normalize the cross-efficiency matrix. We can obtain the normalized matrix as follows.
Step 2. Determining the ideal solution as follows,
Step 3. Construct the grey correlation degree matrix between DMU and the ideal solution.
According to the grey correlation analysis, we can calculate the correlation degree between each DMU and the ideal solution as Formula (8) and construct the grey correlation degree matrix as follows.
Step 4. Calculate the weights set of all criteria. The weight
of the
j-th criteria is calculated by Formulas (13) and (14), so we can get the weights set as follows.
Step 5. Calculate the grey correlation degree between each DMU and the ideal solution. The weighted grey correlation degrees between each DMU and the ideal solution by Formula (10) are
From the results of the grey correlation degree, is the largest of them indicate that DMU5 is more similar to the ideal solution, is the smallest of them indicate that the similarity between DMU9 and the ideal solution is smaller than others.
Step 6. Calculate the relative entropy between each DMU and the ideal solution. According to the relative entropy, the weighted relative entropy between each DMU and the ideal solution is as follows.
From the score of the relative entropy, is the smallest of them, which shows that DMU5 is closer to the ideal solution than other DMUs. is the biggest of them, showing that the similarity between DMU9 and the ideal solution is smaller than others.
Step 7. Normalize
and
according to Formula (15).
By combining determined grey correlation degree and relative entropy by Formula (16), we can get the results as follows.
According to the calculation of grey relative degree and relative entropy, first, it can be found that the effective unit is further distinguished, DMU
5 is the most relevant to the ideal solution, and DMU
1, DMU
2, DMU
4, DMU
6, DMU
7, DMU
9 are inferior to DMU
5. Then, with the TOPSIS results, as shown in
Table 4, it reports that the efficiency trends based on relative entropy and TOPSIS evaluation are consistent, but the efficiency change based on relative entropy is more obvious, which is more convincing. In addition, it can be observed that from the perspective of relative entropy,
,
the closeness of the two DMUs is similar. However, the degree of discrimination between DMU
6 and DMU
4 is large by grey correlation analysis, and DMU
6 is obviously closer to the ideal solution than DMU
4. Therefore, the evaluation result obtained from the comprehensive closeness is obviously improved, and the gap between DMU
4 and DMU
6 is increased.
Finally, after comprehensive consideration, the ranking of all the DMUs is DMU5 > DMU7 >DMU3 > DMU6 > DMU4 > DMU1 > DMU8 > DMU2 > DMU11 > DMU12 > DMU10 > DMU9.
In order to assess the ranking merits of our proposed method, we apply different methods to rank DMUs, the ranking results of DMUs are listed in
Table 7.
Table 7 shows that seven DMUs were identified as efficient DMUs by the CCR efficiency scores, which cannot be further discriminated. It also appears that the ranking results of DMUs from these methods are different. Interestingly, the results show that the ranking results of several DMUs remain relatively stable, such as DMU
8, DMU
9, DMU
11. Therefore, it is clear that DMU
9 is an efficient DMU by the CCR efficiency scores, where as all the ranking results in
Table 7 unanimously indicate that DMU
9 performs worst of the 12 DMUs.
In addition, the ranking result of our proposed method is closer to those of the TOPSIS method (Wu et al. [
26]). By comparing the results of the two methods, we find that the order of some DMUs is different, such as DMU
10 and DMU
12.The rank of DMU
12 is higher than DMU
10 in the relative entropy and grey correlations. Furthermore, as shown in
Table 6, DMU
12 is better than DMU
10 under most of the standards. Therefore, considering the comprehensive information, DMU
12 is superior to DMU
10.