Abstract
Control charts represent a very effective tool used for reducing process variability by early detection of the occurrence of assignable causes of variation. 
-charts are applied to detect changes in process mean whereas S-charts are used to detect the same in process variability. Both charts are generally based on the normality assumption. The S-chart utilizes an unbiased estimator of the population standard deviation . However, it is highly affected by any violation of the normality assumption. In this paper, we propose some alternatives of S-charts based on some robust estimate of scale parameters. We will also illustrate the performance of the proposed control chart.
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