Deviation from the targeted value, these include the total loss function and parameter design techniques and Variations with respect to others in the group. 6.1 Quality Strategy Taguchi observed that variation in product specification, is the primary cause for rejection of a product. The cure for this quality loss is to reduce the variation, and effort should be directed toward zero variation, zero defect. This approach is a general methodology by Taguchi in quality control. Since the quality of a product, or process, may be difficult to define in quantitative terms.
Quality is what the customers perceive it to be.
Thus, quality varies from customer to customer, and from product to product. But, in general, lack of product consistency is the major factor in the perception of poor quality. Making the design less sensitive towards influence of uncontrollable factors. Optimizing the product design.