Multivariate Process Monitoring: A New Use for the Biplot

Abstract In this article, we present a method for monitoring multivariate process data based on the Gabriel biplot. In contrast to existing methods that are based on some form of dimension reduction, we use reduction to two dimensions for displaying the state of the process butallthe data for determining whether it is in a state of statistical control. This approach allows us to detect changes in location, variation, and correlational structure accurately yet display a large amount of information concisely. We illustrate the use of the biplot on some examples of industrial data and also discuss some of the many issues related to a practical implementation of the method.