The quadruple moving average control chart for monitoring the process mean.

The moving average (MA) control chart is a memory-type scheme and effective for monitoring small and moderate shifts in the process mean. Several modifications of the MA chart, such as the double MA (DMA) and the triple MA (TMA) charts, have been introduced to improve the detection ability of the MA chart. In the present article, we propose the quadruple MA (QMA) chart for normally distributed data to improve much more the performance of the MA chart for small shifts. Comparing with the existing MA, DMA, TMA, EWMA and DEWMA charts, it is shown that the proposed chart is more effective for small shifts. Furthermore, it is found that the QMA chart is more in-control (IC) robust to non normality than its competitors. Finally, an illustrative example is provided to demonstrate the application of the proposed chart. [ABSTRACT FROM AUTHOR]