Non-normality and combined double sampling and variable sampling interval control charts

A combination of double sampling the X chart and the variable sampling interval of the X chart (DSVSI X chart) increases the sensitivity in the small shift detection. A usual assumption of control charts is that the process observations are normally distributed. However, this assumption may not be true for some processes in the real industry. This paper presented the performance of DSVSIX chart under non-normality and compared it with the Shewhart X chart and the variable parameters X chart. The compared results show that the DSVSI X chart has the best performance in detecting small process mean shifts.