How to control process variability more effectively: the case of a b-complex vitamin production process

Abstract

This paper presents a new procedure for controlling process variability where (i) the quality of the process is determined by more than one quality characteristic, and (ii) the correlations among those quality characteristics must be taken into consideration. The ability of this procedure to detect an abrupt shift of covariance structure is an improvement on the standard practice based on generalised variance. An experience of the production process of the B-complex vitamin is reported to illustrate the merit of the proposed procedure.