Two Process Models in the Economic Design of an X Chart

Studies of the economic design of control charts often involve the modeling of process quality control within a definite cost structure in order to determine parameters of the control scheme which are optimal in a cost sense. In the modeling stage, it is usually convenient to assume that the distribution of the time a process remains in control has the memoryless property. This paper shows, by comparison with an alternative model, that such an assumption may be far from robust.