An Evaluation of Median Rankit Control Charts

The median rankit control chart produced by a quantile approach has been presented in some quality literature to place emphasis on usefulness for a process with non-normal observations. Nevertheless, the ability of the median rankit chart to detect the process change has not been examined. To bridge the gap, the average run length of the median rankit chart that is widely used to assess the performance of control charts is presented. Under the assumption of process observations from the normal distributions or from some non-normal distributions (heavy-tailed symmetric and skewed distributions), this study also compares the median rankit with the individual Shewhart chart and EWMA chart in terms of their average run length.