SECTION 12.1 Summary

• Work is organized in processes, or chains of activities that lead to some result. We use flowcharts and cause-and-effect diagrams to describe processes. Pareto charts and scatterplots can be useful in isolating primary root causes for quality problems.
• All processes have variation. Common cause variation reflects the natural variation inherent in every process. A process exhibiting only common cause variation is said to be in control. Special cause variation is variation inconsistent with common cause variation. Processes influenced by special cause variation are out of control.
• Control charts are statistical devices indicating when the process is in control or when it is affected by special cause variation. Variable control charts are used for monitoring measurements taken on some continuous scale. Attribute control charts are used for monitoring counting data.