Abstract
In this paper, two single control charts, i.e. the Maximum Double Exponentially Weighted Moving Average (Max-DEWMA) and the Sum of Squares Exponentially Weighted Moving Average (SS-DEWMA) control charts, which can simultaneously monitor the process mean and/or variability, are compared. The existing comparison based on average run length (ARL) criterion reveals that the optimal SS-DEWMA chart generally gives more favorable results compared to the optimal Max-DEWMA chart for detecting shifts in the process mean and/or variability. However, an interpretation solely based on ARL can be misleading. Therefore, the main objective of this study is to compare the performances of the two charts by evaluating their median run lengths (MRLs), when the process mean and/or variability shift at various magnitudes. A Monte Carlo simulation is conducted using the Statistical Analysis Software (SAS). Overall, the MRL results are in accordance with the ARL findings.
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