Steps (1–4) The first step is to calculate the root node in order to form the tree structure. The total number of record is 15, as can be seen in Table 6.1 (first column), which goes as follows: (Individual (ID): 1, 2, 3,…, 15). We can use the entropy formula to calculate the root node based on eq. (6.1).
As can be seen clearly in Table 6.1 class column, 11 individuals belong to patient classification and four to healthy. The general status entropy can be calculated based on eq. (6.1):