Interpreting Control Charts

In an earlier module, we introduced Using Run Charts. Control charts add control limits to a run chart. Control limits (analogous to confidence limits) offer more power to detect special cause variation. A control chart can detect special cause events more frequently and more quickly than run charts, although we can still use the typical long run, trend and other run chart rules.

There are dozens of control chart types and each has specific formulas for calculating control limits. A disadvantage of control charts is that they take more skill to prepare. You can draw a run chart on a napkin. Control charting requires sophisticated software. Most statistical programs will make control charts, but programs specifically designed for quality improvement (QI) may be easier to use.

You will learn:

• Recognize a control chart
• Describe the value of control limits in detecting special cause variation
• Recognize the significance of an “in-control” process
• Interpret a typical control chart

Author(s): John Voss, MD

Estimated time to complete: 20 minutes

Credit hours: .25

Method and Medium: Learners participate in the interactive learning modules by correctly answering multiple choice questions dispersed throughout. Learners will be prompted to try again if a question is answered incorrectly.