Quality Advisor

A free online reference for statistical process control, process capability analysis, measurement systems analysis, control chart interpretation, and other quality metrics.

Control charts: Does your data represent a process that is stable and in control?

Control charts are the best way to learn how a process is running. They 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

If you are not sure which chart to use for your data, review the brief descriptions on data analysis tools.

Control charts - See an example of a control chart

Frequently-asked questions about control charts

  1. Which control chart should you use?
  2. Multiple control limits: A long shot, or just a bad slice?
  3. When should you recalculate limits?
  4. Testing a theory about your data

For more on control charts and how they can help you, view a 4-minute video.

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