Multiple means shewhart charts using variable sampling intervals

Abstract

The problem of simultaneously monitoring the means of several variables is investigated using variable sampling intervals between samples. Several sampling strategies are considered where the interval between samples depends upon what is observed in the most recent sample. These strategies are compared with each other and are found to be more efficient than the typical fixed interval control charts in terms of detecting shifts in the target mean . The effect of correlation between variables is also considered.

Keywords:

• Control charts
• quality
• multivariate normal
• average run length