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A new control chart in contaminated data of t-Student distribution for individual observations


Correspondence to: J. L. Alfaro, Facultad de CC, Económicas y Empresariales de Albacete, Universidad de Castilla-La Mancha, Spain. Plaza de la Universidad no 1, 02071, Albacete, Spain.



Control charts are the most popular tool for monitoring production quality. In traditional control charts, it is usually supposed that the observations follow a multivariate normal distribution. Nevertheless, there are many practical applications where the normality assumption is not fulfilled. Furthermore, the performance of these charts in the presence of measurement errors (outliers) in the historical data has been improved using robust control charts when the observations follow a normal distribution. In this paper, we develop a new control chart for t-Student data based on the trimmed T2 control chart (math formula) through the adaptation of the elements of this chart to the case of this distribution. Simulation studies show that a math formula control chart performs better than T2 in t-Student samples for individual observations. Copyright © 2012 John Wiley & Sons, Ltd.