Phase II profile monitoring based on proportional odds models

• We use a proportional odds model to represent the quality of a process or product.
• We develop EWMA-type control charts for monitoring such models (profiles).
• We provide simulation results to show the effectiveness of the proposed charts.
• We propose a method to estimate the changepoint and identify the parameters of change.
• We use a wine example to illustrate the proposed charts and the diagnostic method.

In this article, the quality of a process or product is assumed to be represented by a relationship (or profile) between the response variable and one or more explanatory variables. Due to the characteristic of the response variable, which is both categorical and ordinal, the relationship is better characterized by a proportional odds model. Two MEWMA-type control charts for monitoring such profiles in Phase II monitoring are proposed. Simulation studies are conducted to compare the effectiveness of these two charting schemes. Furthermore, a diagnostic method is employed to estimate the change point location of the process and to identify the parameters of change in the profile. Finally, a real example is used to illustrate the implementation of the proposed charting schemes and the diagnostic method.