Example 14: Assume we have a text collection D of 900 documents from three topics (or three classes), Science, Sports, and Politics. Each class has 300 documents. Each document in D is labeled with one of the topics (classes). We use this collection to perform clustering to find three clus- ters. Note that class/topic labels are not used in clustering. After clustering. we want to measure the effectiveness of the clustering algorithm. Cluster Science Sports | Politics 1 250 20 10 Entropy Purity 0.589 0.893 2 20 180 80 1.198 0.643 3 30 100 210 1.257 0.617 Total 300 300 1.031 0.711