An EWMA-Type Control Chart for Monitoring the Process Mean Using Auxiliary Information

Abstract

Statistical process control (SPC) is an important application of statistics in which the outputs of production processes are monitored. Control charts are an important tool of SPC. A very popular category is the Shewhart's x-chart used to monitor the mean of a process characteristic. Two alternatives to the Shewhart's x-chart are the cumulative sum and exponentially weighted moving average (EWMA) charts which are designed to detect moderate and small shifts in the process mean. Targeting on small and moderate shifts in the process mean, we propose an EWMA-type control chart which utilizes a single auxiliary variable. The regression estimation technique for the mean is used in defining the control structure of the proposed chart. It is shown that the proposed chart is performing better than its univariate and bivariate competitors which are also designed for detecting small shifts.