A robust standard deviation control chart based on square A estimator

The estimates of a standard deviation deteriorate the detection ability of control charts by reason of its high biases when the contaminations are present. This study proposes two kinds of square A estimators based on different screenings and compares the values of their mean squared error with those of existing estimators in diffuse and localized disturbances. The effectiveness of Phase II control charts is evaluated when the estimators are contaminated in Phase I using two kinds of disturbances. The proposed estimators perform the best against disturbances, with their average run lengths and expected average run lengths being closer to those in normal cases compared to other estimators.

Automated summary

This study proposes two types of square A estimators based on different screenings and compares their mean squared errors with existing estimators under different disturbances. The results show that the proposed estimators perform the best against disturbances and are closer to the normal cases.