A Non-parametric Control Chart for Controlling Variability Based on Squared Rank Test

Abstract

Control charts are used to identify the presence of assignable cause of variation in the process. Non-parametric control chart is an emerging area of recent development in the theory of SPC. Its main advantage is that it does not require any knowledge about the underlying distribution of the variable. In this paper a non-parametric control chart for controlling variability has been developed. Its in control state performances have been computed for different distributions and compared with existing Shewhart S chart. Its efficiency to detect shift in variability has been evaluated.