## 4 Discussion  
To further explore the effects of the IVs on the dependent variable, the attribute selection module in WEKA was adopted to analyze the significant variables. The gain ratio (GainRatioAttributeEval) was applied to rank the variables according to their gain ratio. The experimental results in Figure 1 reveal that variables such as HB, BMI, PLT, OP_DAYS, AGE, INR, OP, DBP, and the variables related to liver and renal function have a larger influence on intraoperative blood transfusion.  
First, HB was found to have the greatest effect on preoperative blood preparation, which corresponded with results from other literature [32; 33; 34; 35; 36; 37]. The relationship between decreasing HB levels and the need for an intraoperative blood transfusion was further explored by employing HB as the sole variable to conduct a univariate analysis using the C4.5 classifier. The retrieved classifications were HB \(\leq\) 12.1 g/dL: Y (656.0/172.0), HB \(>\) 12.1 g/dL: N (831.0/268.0) (Y indicates the status of intraoperative blood transfusion). The results of accuracy, sensitivity, specificity, and AUC were 0.677, 0.77, 0.573, and 0.664, respectively.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Classifier** & **Accuracy** & **Sensitivity** & **Specificity** & **AUC** \\ \hline SVM & 71.1\% & 76.6\% & 64.9\% & 70.8\% \\ C4.5 & 71.3\% & 75.5\% & 66.7\% & 73.8\% \\ CART & 71.8\% & 75.6\% & 67.5\% & 73.9\% \\ LGR & 71.7\% & 77.7\% & 65.1\% & 78.3\% \\ \hline \end{tabular}
\end{table}
Table 4: Experimental results for Dataset B.  
\begin{table}
\begin{tabular}{c c c c c} \hline
**Classifier** & **Accuracy** & **Sensitivity** & **Specificity** & **AUC** \\ \hline SVM & 71.1\% & 78.0\% & 63.5\% & 70.7\% \\ C4.5 & 72.2\% & 78.6\% & 65.1\% & 74.5\% \\ CART & 73.1\% & 78.1\% & 67.5\% & 74.3\% \\ LGR & 72.2\% & 78.4\% & 65.4\% & 78.7\% \\ \hline \end{tabular}
\end{table}
Table 5: Experimental results for Dataset C.  
The effect of BMI came second after HB, which was found to be more influential than the other primary factors considered by specialists (e.g., PLT, OP, AGE, and LIVER). Similar to previous findings [14, 15, 38], the evaluation of BMI indicated that patients with a high BMI may require treatment with the same volume of blood loss. Furthermore, a lower PLT (i.e., PLT \(\leq\) 80,000) indicates a high amount of blood loss. This is because poor blood coagulation may be caused by cirrhosis or severe sepsis, which was supported by a previous study reporting that blood preparation may be suitable with a PLT of <100,000 [15].  
Notably, surgical waiting time (OP_DAYS) was also found to have a marked influence mainly on patients with open wounds because the need for an intraoperative blood transfusion is higher for patients who experience continuous blood loss and have longer surgical waiting times [10].  
Next, our study identified AGE as a vital factor for determining whether a blood transfusion should be performed, which is consistent with the findings of many previous studies [3, 9, 10, 11, 12, 20, 23, 26]. Although some previous studies have considered that INR is irrelevant to the need for a blood transfusion, the results of the present study showed that INR is relevant to the need for a blood transfusion.  
Finally, regarding the type of OP, specialists consider that the decision to prepare blood is highly likely to be affected by events that occur during surgery. For instance, most limb operations do not require blood preparation because tourniquets are used when the need for blood preparation increases or for operations with a high risk of bleeding (e.g., spinal, thigh bone, knee, and hip replacement operations).