Fig. 2.

Results of clustering. (a) Dendrogram by Ward method using square Euclidean distance. The appropriate number of clusters seemed 3, shown in the orange line. (b) The age compared among 3 clusters calculated by Ward method. The age of cluster 1 was younger than the other 2 clusters. (c) The frequency of acute medication oral intake was higher in cluster 3 compared to clusters 1 and 2. (d) The ordinal scale of headache occurrence per month was higher in cluster 3 than in clusters 1 and 2. The ordinal scale is as follows. 0, 15–19 days/months; 1, 20–24 days/months; 2, 25–29 days/months; 3, everyday. (e) The elbow chart calculated by k-means +  + , suggesting 3 to 6 is the appropriate number of clusters. (f) The silhouette score was calculated, and that of 3 clusters was highest as 0.4221. (g) The age compared among 3 clusters calculated by k-means +  + . The age of cluster 1 was younger than that of cluster 2, and that of cluster 2 was younger than that of cluster 3. (h) The frequency of acute medication oral intake seemed higher in cluster 3 compared to clusters 1 and 2. Abbreviations: y.o., years old; *, p < 0.050; **, p < 0.010; ***, p < 0.001