George Mason University
Statistical Process Improvement




You could use a Tukey chart, a Moving Range (XmR) or Moving Average.   A Tukey and a Moving Range charts are preferred to Moving Average chart because of their ease of use and tighter control limits than moving Average.

There is no data comparing the performance of Tukey and XmR chart.  Both are appropriate when no assumptions are made regarding the distribution of the observations, both work relatively efficiently.  Tukey chart is based on Stem and Leaf display method used by Tukey.  It provides tight control limits in short data sets with an outlier (a value more than 3 standard deviation away from the mean).  XmR chart cannot do so.  Therefore, we recommend that you use Tukey chart when ever possible. 



This page was last revised on 05/03/2015 by Farrokh Alemi, Ph.D.  This guide to control charts is part of the course on Quality / Process Improvement