An efficient adaptive EWMA control chart for monitoring the process mean

In recent years, the memory-type control chartsexponentially weighted moving average (EWMA) and cumulative sum (CUSUM)along with the adaptive and dual control-charting structures have received considerable attention because of their excellent ability in providing an overall good detection over a range of mean-shift sizes. These adaptive memory-type control charts include the adaptive exponentially weighted moving average (AEWMA), dual CUSUM, and adaptive CUSUM charts. In this paper, we propose a new AEWMA chart for efficiently monitoring the process mean. The idea is to first design an unbiased estimator of the mean shift using the EWMA statistic and then adaptively update the smoothing constant of the EWMA chart. The run length profiles of the proposed AEWMA chart are computed using extensive Monte Carlo simulations. Based on a comprehensive comparative study, it turns out that the proposed AEWMA chart performs better than the existing AEWMA, adaptive CUSUM, dual CUSUM, and Shewhart-CUSUM charts, in terms of offering more balanced protection against mean shifts of different sizes. An example is also used to explain the working of the existing and proposed control charts.