## 4 Experimental Results and Discussion  
Figure 3 shows normalized kurtosis in the form of box plots to better visualize the normal and pathological voice signals for men and women at each /a/, /i/, and /u/ vowel. Overall, normalized kurtosis estimated in pathological signals tends to be larger and more widely distributed than that estimated from normal speech signals. As shown in Figure 3a,b, the normalized kurtosis extracted from the women's /a/ vowel tended to be distributed below zero, while the one from the men's /a/ vowel tended to be close to zero. In the /i/ samples shown in Figure 3c,d, both the women and men's /i/ samples tended to have values less than zero, but the men's /i/ samples tended to have slightly smaller negative values. For both women and men's /u/ samples, shown in Figure 3e,f, the distributions of the four plots are less than zero, and they are almost identical in shape. Figure 4 shows the distributions of normalized skewness extracted from normal and pathological voice signals for men and women in each /a/, /i/, and /u/ vowel. The normalized skewness extracted from a pathological voice has a smaller average value than that extracted from a normal voice, as well as a wider range. The normalized skewness estimated from the women's /a/ samples in Figure 4a,b has a positive mean for both pathological and normal voices, while that estimated from the men's /a/ samples has a negative mean value distribution for both. For Figure 4c, the normalized skewness analyzed in both normal and pathological /i/ samples tended to have a positive mean on both sides. However, it can be seen that the average of the normalized skewness estimated in the normal voice has a positive value, while that of the pathological voice has a negative average value, as shown in Figure 4d. In both Figure 4e,f, the normalized skewness of the normal /u/ voices tends to have a positive mean, while that of pathological /u/ voices tends to have a negative mean. Figure 2: CNN structure [29]. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Activation function & ReLU \\ Kernel size & (2,2) \\ Optimizer & Adam \\ Epoch & 100 \\ Loss function & Cross-entropy \\ Dropout & 0.05 \\ Pooling window & Max pooling (2,2) \\ Neurons at dense layer & 512 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Parameters of the CNN. Figure 3: Distributions of normalized kurtosis in each vowel (*: extreme outlier). Figure 4: Distributions of normalized skewness in each vowel (o: outlier, *: extreme outlier). Table 4 shows that the statistical analyses between normal and pathological voice signals for women and men were performed using a Mann-Whitney's U test for independent samples. Information on the means, minimums, maximums, percentiles, and \(p\) values are presented. The significance level was set at a priority of \(p<0.05\). In Table 4, an asterisk (*) indicates that the \(p\) value is less than 0.05. This means that some parameters are statistically different between normal and pathological voice signals. The Mann-Whitney U test showed a significant difference between normal and pathological voice signals for normalized skewness (\(p=0.000\)) and kurtosis (\(p=0.000\)) for both women and men, except for women's /u/ samples in the case of the normalized kurtosis (\(p=0.051\)). It is clear that these methods are useful and meaningful for classifying pathological voice signals.