Directional Control Schemes for Multivariate Categorical Processes

We consider statistical process control of multivariate categorical processes and propose a Phase II log-linear directional control chart that exploits directional shift information and integrates the monitoring of multivariate categorical processes into the unified framework of multivariate binomial and multivariate multinomial distributions. We also suggest a diagnostic scheme for identifying the shift direction. Both the control chart and the diagnostic approach are simple and easily computed. Numerical simulations and real applications are presented to demonstrate their effectiveness.