Economic designs of constrained EWMA and combined EWMA-(X)over-bar controlschemes

This research presents a comparison between the cost performance of the Exp onentially Weighted Moving Average (EWMA) and the combined EWMA-(X) over ba r control chart schemes. In particular, we explore the impact of constraini ng the in-control average run length on the optimal cost performance of bot h schemes. Methodologically, we incorporate traditional expected cost model s and study the robustness of the two approaches. In general, there appears to be minimal motivation to combine the use of both charts within the same application. The cost model for the combined chart is not a well-behaved f unction, and yields varying optimal parameters when the in-control average run length is constrained.