## 3 Experimental Investigation
### Experimental Results  
Deeper analysis showed that for this dataset there was no big difference between three, four or five words n-grams used so the final experimental results will be presented when the bag of n-grams is created using three words. In Table 6, we can see all calculated measures, which represent the similarity between text \(D_{20}\) (original text) and other texts in the dataset. The variable \(Q_{n}\), where \(n=1,\ldots,5\) is the question number from the original dataset [28]. All values in Table 6 are in percent so the lowest percent means the worst result (texts are not similar), the highest-best (similar). The highest percent has been marked in bold. The highest percent in \(Q_{1}\) analysis were obtained for all measures when \(D_{20}\) was compared to texts \(D_{5}\) and \(D_{17}\). According to the Table 5, the most similar texts to the original are texts \(D_{4}\), \(D_{11}\), \(D_{15}\), \(D_{17}\). All measures get the highest percent when the original text was compared to the \(D_{17}\), which proves that this text is a near copy. The text \(D_{5}\) is marked as light revision, but all measures showed that it is mostly copied text. As we can see, the other near copy texts (\(D_{4}\), \(D_{11}\), \(D_{15}\)) were detected (the highest percent) as a near copy when overlap measure (5) was used alone (\(D_{4}=80\%\), \(D_{11}=66\%\), \(D_{15}=113\%\)). The value of \(D_{15}\) is higher than \(100\%\), because the original text and \(D_{15}\) fully overlap and some n-grams in original text were even mentioned a few times more. In this case, it meant that these two texts were totally similar. If we look to the \(Q_{2}\) answers' text similarity results, we can see that the highest percent is obtained with text \(D_{1}\) and \(D_{19}\) using the overlap measure. According to Table 5, the heavy copies are \(D_{1}\), \(D_{8}\), and \(D_{18}\). So the only one overlap measure can confirm just one near copy text similarity (\(D_{1}=100\%\)) and light revision (\(D_{19}=81\%\)). Neither measure detected the similarity of text \(D_{18}\), all of them got \(0\%\). Deeper analysis showed that it was some a mistake given in dataset description because looking at the \(D_{18}\) text and comparing it with the original text it was confirmed that these two texts cannot be marked as a near copy because the text is totally different. The results of questions \(Q_{1}\) and \(Q_{2}\) answers' text similarity are presented using SOM (Figure 5) [24]. The color scale from white to black in cells means the values of the U-matrix [22]. The lighter color means that the distance between some data is short and the dark otherwise. The pie charts represent the texts of the dataset. If the dataset items are very similar among each other, they will fall to the same cell (one pie chart divided to pieces). As we can see in Figure 5a, the texts \(D_{5},D_{17},D_{20}\) fall in the same cell so it means that these two texts are similar to the original text \(D_{20}\), that was earlier proved by calculating similarity measures. The other texts also make some groups or fall to the same cell. For example, according to the Table 5, the texts \(D_{2},D_{6},D_{10},D_{16}\) are non-copies so in SOM their fall out in the same cell. Using SOM, we can easily identify which texts are similar to each other. In the right side of Figure 5b, the near copy and light revision texts \(D_{1},D_{4},D_{5},D_{8},D_{12},D_{19}\) are located near original text \(D_{20}\). It also confirms that these texts are the most similar to the original text. Figure 4: The size of the obtained bag of words. The results of \(Q_{3}\) answers texts showed that the highest percent according to the all measures were obtained when the original text was compared to the texts \(D_{2}\) (near copy) and \(D_{9}\) (light revision). The same results as the previous question were found; the highest percent when the overlap measure was used (\(D_{2}=92\%,D_{9}=79\%\)).