Six Sigma Fundamentals: A Complete Introduction to the System, Methods, and Tools

CT stands for critical to, and this characteristic is always a function of the Y = f(x), where Y is the product requirement that impacts quality delivery or cost, and f(x) is one of the vital few process variables that can influence the Y. Another way to view this relationship is to think of Y as the dependent variable and x as the independent variables (factors) that define Y. In other words, as the experimenter defines and understands the x or multiple xs, the better the chance that the Y will be understood, controlled or predicted. On the other hand, CTY is a visual representation of the individual levels of the product. It must be remembered that both the CTX and CTY trees give the opportunity to select the strategy for improvement. Whereas the CTY will help in the area of defect opportunity, the CTX will help in controlling the opportunities in the process. Therefore, it is imperative that we understand both trees, as they will guide us to better results in our analysis. For example, if we consider the Ys and Xs involved in a good meal the CTY and CTX trees will look like: A good meal = Y = service, quality, price, location, ambiance and so on. Now if we take the quality of food as our new Y then we have. Quality of food as the new Y= freshness, wait time for meal, preparation, presentation and so on. On the CD we also have a similar example of cascading the requirements.