Constable, Gordon K.; Cleary, Michael J.; Zhang, Gongxu (1987, ASQC) Wright State University, Dayton OH; Beijing Institute of Post and Telecommunications, Beijing, China
A unit is normally processed through several operations before it becomes a final product. At a particular stage of production (operation), there is an "overall quality" of the product due to the preceding operations, and a "specific quality" about to be imparted to the product at the current operation. If the previous operations affect the quality independently of the current operation, the quality imparted by the current operation is simply additive. However, if the quality of the prior operations affect the quality imparted by the current operation, the quality imparted by the current operation is dependent and is not simply additive. The standard Shewhart control charts can be used to control the overall quality and to control the specific quality of an independent operation, but it cannot discriminate between the quality imparted by prior operations and that imparted by a current operation where they are dependent. The Cause-Selecting chart proposed by Professor Gongxu Zhang is one method of dealing with this problem. This paper will present the concepts of Cause-Selecting charts and illustrate them with an example.