The Efficiency of the VSI Exponentially Weighted Moving Average Median Control Chart

In the literature, median type control charts have been widely investigated as easy and efficient means to monitor the process mean when observations are from a normal distribution. In this work, a Variable Sampling Interval (VSI) Exponentially Weighted Moving Average (EWMA) median control chart is proposed and studied. A Markov chain method is used to obtain optimal designs and evaluate the statistical performance of the proposed chart. Furthermore, practical guidelines and comparisons with the basic EWMA median control chart are provided. Results show that the proposed chart is considerably more efficient than the basic EWMA median control chart. Finally, the implementation of the proposed chart is illustrated with an example in the food production process.

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