When monitoring a variable x in statistical process control, it is necessary to monitor both the mean and variability. Recently, it is found that, if both the mean shift δμ and standard deviation shift δσ follow the uniform distribution, many control charts with different complicacy are...

The EWMA control chart is used to detect small shifts in a process. It has been shown that, for certain values of the smoothing parameter, the EWMA chart for the mean is robust to non normality. In this article, we examine the case of non normality in the EWMA charts for the dispersion. It is...

Traditional statistical process control charts assume that observations are independent and normally distributed about some mean. We investigate the robustness of traditional charts to data correlation when the correlation can be described by an ARMA(1,1) model. We compare the performance of the...

Adaptive control charts deliver significantly better performances than that of static control charts. However, the frequent switches between sampling interval lengths and/or between sample sizes can be a complicating factor in the administration of these charts. This factor is totally absent...

A modified median chart with estimated control limits is proposed for monitoring the mean value of a normal process. The estimates for the nominal process parameters used to set up the control limits in Phase I are the average of the sample medians and the average of the sample ranges of m...

Most processes involve more than one process/product output variable, multiple process input/regulatory variables, and a category of noise variables, which consists of factors not considered in the model, or those external to the process. Since output variables are not necessarily independent of...

Purpose – The majority of quality control charts are employed for normally distributed data. In reality this assumption is not always valid, as an alternative the Burr distribution is considered here. Design/methodology/approach – Having previously derived integral equations for the average...