The Psychology of Quality and More

A Toolbook for Quality Improvement and Problem Solving (contents)

Control Chart: When to use it

The Quality Toolbook > Control Chart > When to use it

When to use it | How to understand it | Example | How to do it | Practical variations

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When to use it

• Use when investigating a process, to determine whether it is in a state of statistical control and thus whether actions are required to bring the process under control.
• Use it to differentiate between special and common causes of variation, identifying the special causes which need to be addressed first.
• Use it to detect statistically significant trends in measurements; for example, to identify when and by how much a change to the process has improved it.
• Use it as an ongoing 'health' measure of a process, to help spot problems before they become significant.
• It is only practical to use it when regular measurements of a process can be made. Typically this is in processes that repeat within a reasonably short space of time.

Fig. 1. Using the Control Chart in problem solving

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