Meerveranderlike Statistiese Kwaliteitsbeheer

Abstract

Multivariate control charts are a relatively new approach in statistical process control. These charts have the advantage that a process functioning precisely to standard will be stopped less often mistakenly than in the case where univariate charts are used. The mutual relationships between variables are considered in the construction of the control limits, which is not the case with the univariate approach. The above-mentioned advantages have been confirmed by simulation studies. The robustness of univariate and multivariate control charts was investigated in respect of a process functioning under normal and varying circumstances. Changes were brought about in the process mean and the covariance matrix. The robustness of the different approaches for deviations from the theoretical assumption of normality was investigated. For this purpose, data were generated from the rectangular and the exponential distributions. Recommendations are made for the use of different multivariate control charts under different circumstances.