## 5 Results and Discussion
### Results of Outlier Handling and Sample Size Determination Using Coefficient of Variation (CV)
#### 5.1.1 Outlier Handling and Sample Size Determination for CF4 Tier 3 DRE Data  
For CF4 gas, 44 Tier 3 DRE data were used, and the sample size was determined after handling outliers in each case (Table 4). The value corresponding to the third quartile (Q3) of the CF4 gas DRE values was found to be 0.969, while the value corresponding to the first quartile (Q1) was found to be 0.924. IQR for Q3 minus Q1 was found to be 0.046, while the figure considering 1.5 times the IQR was found to be 0.069. Taking these values into account, the DRE values for CF4 gas were determined as outliers if they were higher than 1.039 or lower than 0.856.  
The results of the Tier 3 DRE values for CF4 gas according to the case of outlier handling are shown in Table 5. In Case 1, where existing data were used, the mean was 0.921, which is the lowest among all the three cases, and the standard deviation was the highest. In Case 2, where outliers were removed, the sample size decreased by eight compared to the original; here, the mean was 0.961, which is the highest, while the standard deviation was 0.020, which is the lowest. In Case 3, where outliers were adjusted to extreme values, the mean and standard deviation values were at intermediate levels for Case 1 and Case 2.  
For validation, we checked the characteristics of the handled outliers. The characteristic information of the current data is scrubber, and all eight of the handled outliers had burn-type attributes. Therefore, we checked the difference in outliers by including only burn-type scrubbers in the CF4 Tier 3 DRE values (Table 6).  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Classification** & **Value** \\ \hline Q3(75 th Percentile) & 0.969 \\ Q1(25 th Percentile) & 0.924 \\ IQR & 0.046 \\ IQR \(\times\) 1.5 & 0.069 \\ Maximum(Q3 + 1.5 \(\times\) IQR) & 1.039 \\ Minimum(Q1 - 1.5 \(\times\) IQR) & 0.856 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Resources for handling outliers in CF4 Tier 3 DREs.  
For the CF4 gas DRE values, Q3 was found to be 0.938, while Q1 was 0.775 when including only the burn-type scrubbers. IQR for Q3 minus Q1 was 0.163, while the figure considering 1.5 times the IQR was 0.244. Based on these values, the DRE values for burn-type scrubbers in CF4 gas were considered as outliers if they exceeded 1.182 or were less than 0.531.  
After applying the outlier criteria to review the DRE values obtained for the burn-type scrubber, it was found that none of the values met the outlier criteria. The mean value of the CF4 burn-type DREs was 0.843 (which is lower than the overall mean value of CF4 DREs), and their standard deviation was relatively large at 0.115 (which is within the characteristic range of CF4 burn type). This result indicates that there were no outliers that were handled. It also suggests that differences may occur depending on the presence of information about the scrubber type when processing DRE data. Due to the limitations existing in collecting relevant information from the perspective of data processing, we assume that there is no prior information on the relevant data and determine the sample size based on data processing and CV distribution.  
Based on the outlier criteria, the sample size of CF4 DREs was determined using CV values, and the results are shown in Table 7. Based on the outlier criteria, the sample size was 337 for Case 1, 17 for Case 2, and 85 for Case 3. These results show that Cases 2 and 3 had relatively smaller sample sizes compared to Case 1, as outliers were treated and adjusted.