A novel single composite Shewhart‐EWMA control chart for monitoring the process mean

Abstract

AbstractStatistical process monitoring (SPM) literature recommends the combination of Shewhart and exponentially weighted moving average (EWMA) schemes to improve the ability of the standalone Shewhart and EWMA monitoring schemes in detecting small to large shifts. The resulting scheme is named combined (or composite) Shewhart‐EWMA (CSEWMA) scheme. In this paper, a new single composite Shewhart‐EWMA (denoted as SCSEWMA) scheme for monitoring the mean when the process parameters are known or unknown is proposed using an additive weighted model. The flexibility of the proposed scheme is made possible by an additional weighing parameter that regulates its sensitivity towards shifts of different sizes. The new scheme is compared to the existing Shewhart, EWMA and CSEWMA schemes, and the results reveal the superiority of the proposed scheme over the latter schemes. Simulated and real‐life data are used to demonstrate the application and implementation of the proposed scheme.