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A performance evaluation matrix is based on questionnaires collected from users or customers to pinpoint the performance of a system operation and furthermore to locate the items that need to be improved to upgrade the performance of system operations. To achieve this, this article proposes a discrimination index and applies statistics inference to deduce confidence intervals of the discrimination index. Meanwhile, we refer to Buckley’s fuzzy testing method to construct a fuzzy affiliation function and address a fuzzy evaluation criterion for exploring the items considered critical to quality to overcome the complicated problems of the questionnaires’ sampling error and interviewees’ fuzzy linguistics. The advantages of the method in this article are that it keeps the simple filling pattern of Likert’s scale and provides efficacy of data collection. Subsequently, we reduce the fuzzy linguistics and questionnaires’ sampling error by statistics inference and fuzzy hypothesis testing. Finally, we use a case study with the computer-assisted language learning system to demonstrate an application of the proposed method.

The growing popularity of do-it-yourself (DIY) projects has increased the penetration of hand tools devices into the market. This paper thus conducts a case study on ratchet torque wrenches and develops an assessment and verification model of process quality as a means of assisting hand tool manufacturers in managing the quality of ratchet torque wrench products and promoting the on-going development in the hand tool industry. We first propose the process quality index (PQI) that can directly determine a precise level of quality based on the relationship between various process capability indices and Six Sigma quality levels. Using inference, we further develop a testing model of PQI to evaluate the quality level reached of process performance. The present case study is investigated to illustrate the practical applicability of the proposed method. We believe that the proposed model will facilitate the production of high-value products and thereby enhance the competitive advantage of firms in Taiwan.