What is it?

Control charts (also called process behavior charts or Shewhart charts) are graphic tools originally developed by statistician Walter Shewhart. The best way to learn how a process is behaving is to plot statistical data over time with a central line and control limits. Control charts are used to reduce the chance of making one of two kinds of mistakes:

1. Overcontrolling
   Also called a Type I error, this refers to adjusting the process when nothing out of the ordinary has occurred.
2. Undercontrolling
   Also called a Type II error, this refers to the failure to adjust the process when something out of the ordinary has occurred.

Why is it important?

Control charts identify the two types of variation present in a system, special and common, so the proper improvement action can be taken. Use control charts first to assess stability and learn what kind of action to plan next. Once you have implemented an improvement action, the control chart monitors the system in order to see if the improvement action has been effective.

How can PQ help?

PQ Systems provides training in the use of control charts and software to help you create and use control charts.