Fig. 5. Heatmap with dendrogram of 39 selected questions based on the Euclidean distance. The y-axis represents 39 selected questions and x-axis represents each subject. The colors in the heatmap represent answers range from 1 to 5 (shown in color bar). The circles in the x-axis indicate different clusters resulted from K-means clustering; GREen circle (Cluster 1); orange circle (Cluster 2); blue circle (Cluster 3).