Product design requires careful consideration of many factors. However, it is difficult for many developers to design a product that will satisfy everyone, because they do not know the answers to questions such as “What causes large number of people to like a specific product?” “What fascinates them about the product?” or “Which part or element of the design makes it attractive?” In general, people like “usable” products, but it is difficult to know what makes certain products easy to use. This paper proposes a method for investigating “ease-of-use” by means of a fuzzy decision tree. It builds a decision tree based on the results of a questionnaire, which determines user’s product impressions, and helps to uncover the major factors that affect the product’s “ease-of-use.” In this paper, we analyzed golf clubs and investigated the factors that determine their particular ease-of-hitting, which is concerned with the ability to hit golf balls easily. As a result, we obtained some reliable rules affecting user impressions using the fuzzy decision tree built from the questionnaire results.

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