Rule induction in data mining: effect of ordinal scales

Many classi®cation tasks can be viewed as ordinal. Use of numeric information usually provides possibilities for more powerful analysis than ordinal data. On the other hand, ordinal data allows more powerful analysis when compared to nominal data. It is therefore important not to overlook knowledge about ordinal dependencies in data sets used in data mining. This paper investigates data mining support available from ordinal data. The effect of considering ordinal dependencies in the data set on the overall results of constructing decision trees and induction rules is illustrated. The degree of improved prediction of ordinal over nominal data is demonstrated. When data was very representative and consistent, use of ordinal information reduced the number of ®nal rules with a lower error rate. Data treatment alternatives are presented to deal with data sets having greater imperfections. q 2002 Elsevier Science Ltd. All rights reserved.