QUALITY NOTES: Simultaneous monitoring of univariate and multivariate SPC information using boxplots

We propose a simple control‐charting scheme for simultaneously displaying univariate and multivariate process information. The proposed chart can be used as a diagnostic tool for understanding the nature of out‐of‐control conditions in multivariate statistical process control (SPC). The chart is easy to implement and interpret. Two examples are given for illustration purposes.