Abstract: A model of threcway decision-theoretic rough sets (DTRS) was presented based on the Bayesian decision theory. Based on the minimum expected risk, a detailed formulation of DTRS was given. Different types of errors in several probability intervals were examined. The conditions under which DTRS thruway method is superior to the Pawlak three-way method and two-way method were identified. DTRS threcway model was discussed for solving the practical decision problems.

Key words: Decision-theoretic rough set theory, Bayesian decision procedure, Three-way decision making, Two-way decision making