Fig. 8.

In order to determine the optimal number of clusters in a signature for a multi-class problem the error rate was measured as the number of clusters in the signature was varied. Figure (a), shows the least error with a 4 cluster signature. Figure (b), shows the sensitivity (true positive rate) in green and specificity (true negative rate) in yellow for the 4-class classification experiment of normal (N), reticular (R), honeycombing (H), and emphysema (E). Figure c, shows the sensitivity (true positive rate) in green and specificity (true negative rate) in yellow for the 5-class classification experiment of normal (N), ground glass (G), reticular (R), honeycombing (H), and emphysema (E). Note that the sensitivity for honeycombing class remains about the same for the 4 and 5 class problem. However, note that the sensitivity of the reticular class is significantly reduced in the 5 class problem - this is because of the similarity between the ground glass and reticular classes, detailed in the confusion matrices in Table 1 and Table 2