Abstract: To obtain the importance ratings of the customer requirements’ improvements for product planning house of quality(PPHOQ), a method based on rough set theory is proposed. Because the requirements in the customer investigations of PPHOQ are uncertain and fuzzy, based on some related methods of relative reduction and relative core in rough set theory, the customer requirements of PPHOQ are determined. Using the method of relative positive field in rough set, a method of determining the fundamental importance ratings of the customer requirements is proposed. The efficiency and risk analysis are implemented on the achievement of the improvement ratio of customer requirement’s satisfaction, a formula of calculating the importance rating of achieving the improvement ratio of customer requirement’s satisfaction is presented. Based on a combination of the fundamental importance rating of customer requirement, the importance rating of achieving the improvement ratio of customer requirement’s satisfaction and “sale point of customer requirement”, a method of determining the importance rating of the customer requirements’ improvements is proposed. A case study of product improvement of fully automatic washing machines in a company is provided to illustrate the application of the presented method.

Key words: Customer requirement, Importance rating, Quality function deployment, Rough set