4.2. Normalization of Index Values Based on Segment Mapping
Different evaluation indicators usually have different dimensions and orders of magnitude, and the data of the indicators cannot be used for comparison directly. In order to ensure the objectivity and scientificity of the comparison results, it is necessary to standardize the original value of each evaluation object. Through standardized processing, the unit of different attribute indexes is eliminated, and the standardized evaluation index data is additive and comparable. In general, the original data are linearly transformed to map the data to [0,1] or [−1,1]. The methods commonly used for index value standardization are the min-max standardization [
37,
38], z-score standardization [
2], maximum value standardization [
39], and the specific gravity method [
10]. Taking the dimensionless processing of the sequences
x1,
x2, …,
xn as an example, using the min-max standardization method, the normalized equations of the positive and negative type indexes are expressed as Formulas (1) and (2) [
40]:
The calculation formula of the z-score standardization method is as follows [
2]:
In Formula (3),
and
are calculated as follows [
2]:
The calculation formula using the maximum value normalization method is as follows [
39]:
The calculation formula of the standardized method using the specific gravity method is as follows [
10]:
When the difference between the maximum value and the minimum value of the index value is not too large, the normalized mapping data of the method is not affected by the range, the data distribution is basically uniform and normal. Moreover, the mapping data of different attribute indexes have strong comparability, and the comprehensive evaluation value has more comprehensive representativeness and comprehensiveness. When the range of the evaluation value under an attribute index is too large, the traditional normalization will cause a problem where the comprehensive evaluation result is too greatly affected by some indexes, and it cannot comprehensively reflect the situation of the comprehensive evaluation. Taking the indexes selected for regional logistics competitiveness as an example, there is a large gap between the maximum value of the attribute indexes, the median value, and the minimum value; the ratios of the lowest maximum value and the median value, maximum value, and minimum value of the 23 indexes selected are 2.1 times and 13 times, and the maximum and minimum values of other indexes are tens, hundreds, or even more thousand times. For example, the gap between the maximum value and the minimum value of the express delivery volume, the total import, and export volume, and other indexes in 2017 reached about 1786 and 2473 times, respectively; the normalized median corresponding to about 0.5 is reasonable, which is actually less than 0.05, which is obviously contrary to common sense. In this case, compared with the maximum value, the difference between the smaller evaluation values is almost indistinguishable; even if there is a multiple difference, the score after comparing with the extreme value can be almost ignored. For example, the maximum value of an index is 10,000, and the smaller values (which ranges from 0 to 1000) are in the interval [0,0.1] after normalization. The proportion of the values in this interval may be more, leading to low differentiation, which makes evaluation difficult. The comprehensive score becomes a comparison of whether there is a specialty. If there are no maximum or near-maximum scores, other scores become extremely difficult to determine, making the comprehensive evaluation appear to be a partial phenomenon. This kind of evaluation violates the original intention of the comprehensive evaluation, and it cannot systematically reflect the comprehensive level of the evaluation object. The standardization of the segmented mapping of the index can avoid the problem where the normalized smaller value is extremely weakened due to the existence of the maximum value.
Taking index Cj as an example, we normalize the index value under index Cj to a [0,1] interval value, and we divide the [0,1] interval value into 11 grades, which respectively represent extremely weak [0,0.05), very weak [0.05,0.15), weaker [0.15,0.25), weak [0.25,0.35), lower middle [0.35, 0.45), medium [0.45,0.55), upper middle [0.55,0.65), strong [0.65,0.75), stronger [0.75,0.85), very strong [0.85,0.95), and extremely strong [0.95,1]. The original index values are sorted according to size, and the median of all values is used as the reference point corresponding to the medium evaluation value, which is called the middle reference point; the reference value of the middle reference point is the middle value 0.5 of the scale interval [0,1], and the median of the first half of the evaluation value is taken as the reference point of the upstream and middle evaluation values, which is called the upper and middle reference point. The reference value of the upper and middle reference point is the middle value of the scale interval [0.5,1], which is 0.75 (critical values of strong and stronger). The median of the second half of the evaluation value is taken as the reference point of the middle and downstream evaluation values, which is called the middle and downstream reference point. The reference value of the middle and downstream reference point is the middle value of the scale interval [0,0.5], which is 0.25 (critical values of weaker and weak). According to the setting of the reference points, there are four mapping intervals corresponding to the original evaluation values, and the number of intervals from high to low are [0.75,1], [0.5,0.75], [0.25,0.5], and [0,0.25]. In order to determine the distribution of the actual evaluation values and whether the extreme value of the evaluation value of the index is too large, this paper compared the three dividing points (0.75, 0.5, 0.25) of the mapping interval with the normalized values of the quartiles. The original evaluation value of the index Cj was recorded as (i = 1,2,3…,m; j = 1,2,3…,n), which has three-quarters quantiles, median, and quarter quantiles recorded as ()Q3, ()Q2 and ()Q1, respectively; correspondingly, the original evaluation data of Cj were divided into four intervals with the quartile as the cut-off point, and the intervals are [()Q3,()max], [()Q2,()Q3], [()Q1,()Q2], [()min,()Q1] from large to small. In order to reduce the influence range of the maximum value on data normalization and make the normalization ratio better map the difference of the original value, the original value was divided into the first half (the part with large value) and the second half (the part with small value) with the median as the boundary. The first half uses the ratio of three-quarters quantiles of each index to the maximum value, as well as the ratio of the median to the maximum value as the judgment value, and compares it with the reference values of 0.75 and 0.5, respectively. The second half uses the ratio of quarter quantiles of each index to the median value as the judgment value, and compares it with the reference value of 0.5. When the judgment value is greater than or equal to the reference value, it means that the data range is not big, and there is no case that the maximum value is too large, meaning there is no need for interval conversion. When the judgment value is less than the reference value, it means that the data range is too large. In order to make the evaluation value more comparable, it is necessary to perform a rational mapping process on each evaluation value of the original range that is too large to make it more reasonable to map to the corresponding mapping interval.
Assuming that the original interval of the h-th segment of the evaluation target index value under the
Cj index is [((
)
min)
h,((
)
max)
h], the corresponding mapping interval is ((
)
min)
h,((
)
max)
h], the value after the mapping is (
aij)
h, and the mapping formula of (
aij)
h is as follows:
According to the normalized value distribution range of the index, the mapping value of the maximum evaluation value under the index
Cj is 1, and the mapping value of the minimum evaluation value is converted according to the middle and lower reference points (quarter quantiles). Assuming that the evaluation value of the middle and downstream reference points of the index
Cj is (
Rj)
Q1, the minimum value of
Cj is (
Rj)
min, the reference value of the middle and downstream reference points is (
Sj)
Q1, and the reference value of the minimum value is recorded as (
Sj)
min. The formula for (
Si)
min is as follows:
Taking the index Cj as an example, represents the original index value of the j-th attribute of the i-th evaluated object, where the maximum value of the evaluation value under the Cj index is ()max, the three-quarters quantiles is ()Q3, the median is ()Q2, the quarter quantiles is ()Q1, and the minimum is ()min. The original evaluation data is arranged from big to small and divided into four intervals according to the quartile: They are [()Q3,()max], [()Q2,()Q3], [()Q1,()Q2], [()min,()Q1] in order from big to small. Here, represents the normalized original value of the index of the j-th attribute of the i-th evaluated object, according to the previous normalization processing method of the index value based on the segmentation mapping. The original evaluation value is judged between the partitions, and the normalized processing of the evaluation values is as follows:
(1) For the data in the interval [(
)
Q3,(
)
max], when (
)
Q3/(
)
max >= 0.75, no mapping processing is performed. When (
)
Q3/(
)
max < 0.75, the maximum value is found to be too large, and the normalization processing is as follows:
(2) For the data in the interval [(
)
Q2, (
)
Q3], when (
)
Q2/(
)
max >= 0.5, no mapping processing is performed; When (
)
Q2/(
)
max < 0.5, the maximum value is found to be is too large, and the normalization processing is as follows:
(3) For the data in the interval [(
)
Q1, (
)
Q2], when (
)
Q1/(
)
Q2 >= 0.5, no mapping processing is performed; When (
)
Q1/(
)
Q2 < 0.5, the maximum value is found to be too large, and the normalization processing is as follows:
(4) For the data in the interval [(
)
min, (
)
Q1], when (
)
Q1/(
)
Q2 >= 0.5, no mapping processing is performed; When (
)
Q1/(
)
Q2 < 0.5, the maximum value is found to be too large, and the normalization processing is as follows:
4.3. Method for Determining Attribute Index Weights Based on an Improved Analytic Hierarchy Process
The analytic hierarchy process (AHP) is a multi-objective decision analysis technology combining both qualitative and quantitative analyses proposed by American operations researcher Saaty [
41]. This method takes the form of a proportional scale and makes full use of human experience and judgment. It compares the relative importance of relevant factors at the same level and combines the measures of decision-making objectives from the top to the bottom [
35]. Compared with the objective weighting method, the analytic hierarchy process scientifically and reasonably reflects the subjective judgment of the evaluator; this method integrates various qualitative and quantitative factors, and it has certain reliability and validity. Among various studies in different fields, the analytic hierarchy process (AHP) is regarded as the most effective and commonly used multiple-criteria decision-making (MCDM) method [
42]. The analytic hierarchy process (AHP) is particularly suitable for the analysis and decision-making of complex systems with multiple objectives, multiple levels, multiple factors, and multiple schemes due to its systemic, flexible, and practical characteristics [
43]. However, the scientificity and accuracy of an evaluation using the analytic hierarchy process should be based on reasonable scales and clear logics. The selection of appropriate scales and clear logical relationship judgments are the pre-requisites for the appraisers to make correct judgments.
In the scale setting, the analytic hierarchy process generally uses the numbers 1–9 and their reciprocals as the scale to establish the judgment matrix. According to the scale of 1–9, 1 means equally important, 3 means slightly important, 5 means obviously important, 7 means strongly important, and 9 is extremely important, while 2, 4, 6, and 8 are the median values of neighboring judgments. This scale is simple and clear, but there are some problems, and sometimes the judgment result is far from objective. For example, suppose there are three indexes: A, B, and C. Here, A is slightly more important than B (A/B = 3), and B is slightly more important than C (B/C = 3). The calculation shows that A is more extreme than C in importance (A/C = 9); however, according to the expert’s judgment in the actual research, the importance of A over C will generally be near the position of significant importance (A/C = 5). Moreover, the actual judgment and calculation results are inconsistent, which destroys the consistency of the matrix. In addition to the 1–9 scale, a variety of scales has been proposed, such as the 0 to 2 three-scale method, the −1 to 1 three-scale method, the five-scale system, the 9/9–9/1 scale, the 10/10–18/2 scale, the exponential scale, etc. [
44]. Xu Zeshui (2000) [
44] compared a variety of scales and found that the 10/10–18/2 scale shows obvious superiority in the accurate weight calculation, and the obtained results are more accurate. The results show that different scale systems are inherently inconsistent.
In terms of logical judgment, the evaluator needs to accurately determine the logical relationship between the indexes. The more evaluation indexes there are, the easier it is for people to compare the indexes, and the more difficult it is to determine the logical relationship between the indexes. When there are many indexes at the same level, the judgments given by the evaluators may even conflict with each other, causing serious inconsistencies in the judgment matrix. However, the consistency of the judgment matrix is a necessary condition for using the analytic hierarchy process. In the application of this method, the inherent defect of the consistency of the judgment matrix has not been overcome; especially when the compared elements are more than 10, the application of this method is even more inaccurate [
45].
Aiming at the problem of consistency of judgment matrix constructed by the analytic hierarchy process, this paper proposes an improved analytic hierarchy process method to solve the index weight. The method mainly involves using the chart method to judge the logical relationship between indexes, making the index judgment matrix fully meet the matrix consistency, improving the limitation of the inaccurate method when there are too many elements to be compared, improving the scientificity and logicality of the AHP, using the idea of a dynamic scale decision to establish the scale, and obtaining the subjective weight according to the established index hierarchy model. The specific method is as follows:
(1) Calculate the relationship between indexes through the index importance level classification table
The traditional analytic hierarchy process was used to determine the index weights. First, the evaluation index system was constructed, then the importance of all elements in the next layer compared to the previous layer was compared in pairs, and finally the judgment matrix was constructed. Due to the logical deviation of subjective judgment, the analytic hierarchy process will check the consistency of the judgment matrix. If the test result is within a certain reasonable range, the consistency of the judgment matrix is considered to be is acceptable, and there is no need to adjust the judgment matrix. If the test results are not within a reasonable range, the relationship between the indexes needs to be corrected, and a new judgment matrix is obtained by recalculation. In order to make the comparison between indexes more accurate, all indexes are classified by grade. The grade number does not represent the actual value size, only the importance. The larger the grade value is, the more important the index is. In order to facilitate the conversion, the number of levels of importance and the level of the analytic hierarchy process are the same. Based on the idea of sorting, the indexes were identified in the index importance level classification table by using a check form; after checking, the indexes of different categories were balanced to obtain the final index importance level classification table. Assuming that the index layer to which the subsystem level index B1 belongs has four evaluation indexes of
C1,
C2,
C3, and
C4, experts give their importance levels of 9, 5, 3, and 7 respectively. The classification table of the importance of the indexes is given in
Table 2.
According to the importance grade judgment in the classification table of importance level of indexes, the relationship between the two indexes was calculated. Taking
Ci and
Cj as examples, assuming
Ci =
Pi and
Cj =
Pj, sgn(
Pi −
Pj) is a symbolic function, and
is an arbitrarily small positive real number (make sure that the base of the exponential function is greater than zero). According to the calculation logic of a traditional AHP index comparison, the relationship between
Ci and
Cj is as follows:
Taking
C1 and
C2 for example,
C1 = 9, and
C2 = 5. According to Formula (13), it is calculated as follows:
(2) Establishing scale of exponential function
Using the result of the non-deterministic exponential function
y =
ux (
u > 1,
x ≥ 0) and its reciprocal as the scale to establish a judgment matrix,
u > 1 makes the exponential function a monotonically increasing function. In order to facilitate identification and comparison, we let the value of the index
x be a natural number. When
x = 0 and
u0 = 1, it means that they are equally important. According to the difference in the importance of the scale and the requirements of the degree of discrimination, the interval of the base number and the index should be determined reasonably. If the maximum value of x is g, then g + 1 is used to represent the scale series. When g = 8, the set of
ax corresponds to a scale of 1–9. Assuming that the values of base u are 1.1, 1.2, 1.3, 1.4, and 1.5, the corresponding scale values are shown in
Table 3.
(3) Constructing the judgment matrix through scale transformation
Comparing the meaning of the index scales corresponding to the AHP scale classification table in
Table 3, the relationship between the two indexes is that
C1 is slightly more important than
C2. According to the calculation and analysis of the index relationship, if the experts think that the meaning of the index scale description corresponding to the calculation result is far from the original judgment, they can adjust the judgment in
Table 3 and then calculate it again until the judgment is basically consistent.
According to the meaning of the exponential function, the calculation result of the relationship between
Ci and
Cj is equal to the exponent x of the scale function, and the calculation formula is as follows:
Substituting the result and index scales, the scale conversion formula is as follows:
Taking the evaluation indexes
C1,
C2,
C3, ……,
Cn as examples, the judgment matrix of the evaluation indexes is established as follows:
(4) Calculating the weight of the evaluation index
The weight vector
Wj of the evaluation index
Cj is calculated by the sum method as follows:
4.4. Summary of Methods and Steps
Step 1: Establishing the evaluation scheme characterization
First,
represents the original index value of the
j-th attribute of the
i-th evaluation object, and the evaluation scheme characterization is established as shown in
Table 4.
Step 2: Normalizing the index value in sections
If the index is a positive (benefit type) index, the greater the expectation is, the better, and then the index has the maximum polarity and takes the maximum value. If the index is a reverse (cost-type) index, the smaller the expectation is, the better, and then the index has the minimum polarity and takes the minimum value. If the index is a specified value or a medium-sized index, the index has a moderate value polarity, and the specified value or average value is taken. Considering the extreme value of the attribute index, the original data was normalized by using an improved normalization method. Taking the quartile as the dividing point, the original evaluation value was divided into four intervals. According to the ratio and according to the relationship between the ratios of the maximum value of the index (assuming the index is a positive index) and the three-quarters quantiles, the maximum and median, the median and quarter quantiles, and the reference ratio, the data that need to be mapped in sections were transformed to get more scientific and reasonable normalized data.
Step 3: Establishing the scale of the attribute index and calculating the weight of the evaluation index
An improved analytic hierarchy process was used to establish the weights of the evaluation indexes, and the importance difference between the indexes was quantified using the index scale x, in which the index x of
x represents the number of levels of the scale, and the base
represents the cardinal number of the scale. First, the scale series x = p (generally 3, 5, 7, 9 scales are used) of attribute index was determined according to the differentiation, and then the maximum scale a
p was determined according to the difference degree of the least important index and the most important index. Next, the scale values corresponding to different levels of scale were obtained by an exponential function. The degree of importance between the indexes from equal importance to extreme importance is represented by 1(
0),
1,
2,
3,……,
p; conversely, they are represented by their reciprocal. On the basis of the scale value, the importance of indexes was classified with the help of the index importance classification table (
Table 3). The evaluation matrix was constructed based on the classification, and the weight vector of each evaluation index was calculated by Formula (13). Since the relationship of indexes is given according to the importance classification table of indexes, the logic of pairwise comparison of indexes is consistent, and the judgment matrix no longer needs to be checked for consistency.
Step 4: Constructing a normalized weighted evaluation matrix Z
The weight of the index
Cj is
Wj, and the element in the normalized evaluation matrix
Z is
Zij. The calculation formula of
Zij is as follows:
Constructing a normalized weighted evaluation matrix is as follows:
Step 5: Sorting the evaluation objects based on the comprehensive evaluation value
According to the row vector of the weighted evaluation matrix, the comprehensive evaluation value of each evaluated object was calculated, and the comprehensive evaluation value
Zi of the evaluated object
Ai was calculated as follows:
The evaluated objects are sorted according to the size of the comprehensive evaluation value.