A comparative study on the estimators of standard deviation in statistical process control

Abstract

Since the 1930s statistical methods applied to industrial process control have received much attention. Many techniques of statistical process control, such as control chart and process capability analysis, require knowledge of process standard deviation. Therefore, estimation of the process standard deviation plays an important role in statistical process control. In this article, we reviewed four widely used estimators of standard deviation and derived the efficiency of each estimator. Then, these four estimators of standard deviation were compared based on their efficiencies. From the comparative studies, we suggest that if the sample size is greater than or equal to 6, the second, third and fourth estimators may be used to estimate process standard deviation. However, if the sample size is less than or equal to 5, then the third and fourth estimators should be preferred.