## 3 Construction of the Risk Assessment Model
### Set Pair Analysis Method
#### 3.3.1 Comprehensive Ranking Weights  
In the context of risk assessment for determining risk levels, it is necessary to establish the association between the measured values of indicators and the criteria for evaluation levels. In this paper, the degree of association \(\mu_{\mathrm{k}}\) is determined based on the numerical closeness between the measured values of indicators and the criteria for evaluation levels. Accordingly, a corresponding calculation system is established. Assuming that the evaluation criteria for the indicator \(\mathrm{i}\) are divided into \(\mathrm{N}\) levels, the identical discrepancy contrary between the measured value \(\mathrm{x_{i}}\) of the indicator and the reference level \(\mathrm{k}\) is illustrated in Figure 9. The degree of association \(\mu_{\mathrm{ik}}\) is 1 when \(\mathrm{x_{i}}\) falls within the range of level \(\mathrm{k}\). If \(\mathrm{x_{i}}\) is within the range of adjacent level criteria, \(\mu_{\mathrm{ik}}\in[-1,1]\). However, if \(\mathrm{x_{i}}\) falls within the range of non-adjacent level criteria, \(\mu_{\mathrm{ik}}=-1\). According to the above definition, the degree of association \(\mu_{\mathrm{ik}}\) between evaluation indicator \(\mathrm{i}\) and reference level \(\mathrm{k}\) can be calculated using Equation (12):  
\[\mu_{\mathrm{ik}}=\left\{ \begin{array}{ll}1-2\Big{|}\frac{\mathrm{p_{j,k-1} -\mathrm{x_{i}}}}{\mathrm{p_{j,k-1}-\mathrm{p_{j,k-2}}}}&(\mathrm{If\ x_{i}\ belongs\ to\ level\ k-1})\\ 1&(\mathrm{If\ x_{i}\ belongs\ to\ level\ k})\\ 1-2\Big{|}\frac{\mathrm{x_{i}-\mathrm{p_{j,k}}}}{\mathrm{p_{j,k+1}-\mathrm{p_ {j,k}}}}&(\mathrm{If\ x_{i}\ belongs\ to\ level\ k+1})\\ -1&(\mathrm{If\ x_{i}\ belongs\ to\ another\ level})\end{array} \right. \tag{12}\]In the equation, \(x_{i}\) represents the measured value of indicator \(i\), and \(p_{i,k}\) represents the threshold value corresponding to indicator \(i\) for level \(k\), where \(k=1,2,\ldots,N\) represents the risk level. In Section 2.3 of this paper, based on relevant standard specifications and by referencing some existing research achievements, all the indicator evaluation levels were divided into five levels, and their corresponding level criteria were determined. Therefore, when \(N=5\), the degree of association function [30] can be represented as follows:  
\[\mu_{i1}=\left\{ \begin{array}{ll}1&\left(x_{i}\leq p_{i,1}\right)\\ 1&-\frac{2(x_{i}-p_{i,1})}{p_{i,2}-p_{i,1}}&\left(p_{i,1}<x_{i}\leq p_{i,2} \right)\\ -1&\left(x_{i}>p_{i,2}\right)\end{array} \right. \tag{13}\]  
\[\mu_{2}=\left\{ \begin{array}{ll}1-\frac{2(p_{i,1}-x_{i})}{p_{i,1}-p_{i,0}}& \left(x_{i}\leq p_{i,1}\right)\\ 1&\left(p_{i,1}<x_{i}\leq p_{i,2}\right)\\ 1-\frac{2(x_{i}-p_{i,2})}{p_{i,3}-p_{i,2}}&\left(p_{i,2}<x_{i}\leq p_{i,3} \right)\\ -1&\left(x_{i}>p_{i,3}\right)\end{array} \right. \tag{14}\]  
\[\mu_{i3}=\left\{ \begin{array}{ll}-1&\left(x_{i}\leq p_{i,1}\right)\\ 1-\frac{2(p_{i,2}-x_{i})}{p_{i,2}-p_{i,1}}&\left(p_{i,1}<x_{i}\leq p_{i,2} \right)\\ 1&\left(p_{i,2}<x_{i}\leq p_{i,3}\right)\\ 1-\frac{2(x_{i}-p_{i,3})}{p_{i,4}-p_{i,3}}&\left(p_{i,3}<x_{i}\leq p_{i,4} \right)\\ -1&\left(x_{i}>p_{i,4}\right)\end{array} \right. \tag{15}\]  
\[\mu_{i4}=\left\{ \begin{array}{ll}-1&\left(x_{i}\leq p_{i,2}\right)\\ 1-\frac{2(p_{i,3}-x_{i})}{p_{i,3}-p_{i,2}}&\left(p_{i,2}<x_{i}\leq p_{i,3} \right)\\ 1&\left(p_{i,3}<x_{i}\leq p_{i,4}\right)\\ 1-\frac{2(x_{i}-p_{i,4})}{p_{i,5}-p_{i,4}}&\left(p_{i,4}<x_{i}\leq p_{i,5} \right)\end{array} \right. \tag{16}\]  
\[\mu_{i5}=\left\{ \begin{array}{ll}-1&\left(x_{i}\leq p_{i,3}\right)\\ 1-\frac{2(p_{i,4}-x_{i})}{p_{i,4}-p_{i,3}}&\left(p_{i,3}<x_{i}\leq p_{i,4} \right)\\ 1&\left(p_{i,4}<x_{i}\leq p_{i,5}\right)\end{array} \right. \tag{17}\]  
In the equation, \(x_{i}\) represents the measured value of the indicator, and the degree of association for the indicator \(i\) with the five levels are denoted as \(\mu_{i1}\), \(\mu_{i2}\), \(\mu_{i3}\), \(\mu_{i4}\), \(\mu_{i5}\), respectively.