### I. Introduction

### II. Materials and Methods

*no. of operations*, which simply stores the number of times of operations performed on a patient, thereby reducing both the number of null values and the number of fields. And disease codes other than cancer were divided into 19 fields, each of which denotes the number of diseases in each disease group. As a consequence, 65 input fields were created in total. 19 disease groupswere generated according to the Korean Classification of Diseases and 16 treatment groups were also generated according to the ICD-9CM classification. Each kind of cancer was stored into one of the twelve fields.

### III. Results

*duration of admission*(0.074),

*number of consultations*(0.062) and

*treatment group 16*(0.061) (Table 3).

*Treatment group 16*is designated as the miscellaneous diagnostic and therapeutic procedures. The most important factors in predicting the amount paid by insurance were

*duration of admission*(0.091),

*the number of ICU admission*(0.063) and

*the number of consultation*(0.063). Among the variables, physician relative variables such as Doctor ID did not influence on the relative importances.

*number of operations*at the left branch of the tree. Then, the nodes at other levels were split based on

*number of operations*,

*treatment group 16*, and

*treatment group 9*. The number of rules in the resulting rule set was eleven and these rules classified the part of high hospital expense well. For example, consider these rules: IF "(1) days of admission ≥14.5 and (2) days of admission <55.5 and (3) the number of ICU admission <0.5" THEN "3,125,038". The correlation coefficients of the CART models were 0.791 for the total amount of hospital charge and 0.699 for the amount paid by insurance regardless of feature selection. In the CART model for amount paid by insurance, the

*duration of admission*was most important variable also but instead of the

*number of operation*,

*department*was demonstrated as second important variable. The other variables were number of

*ICU admission*and

*treatment group 16*(Fig. 3).