Quality Advisor

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

Any point lying outside the control limits

This is the quickest and easiest test for system stability. Look above the upper control limit and below the lower control limit to see whether any points fall in those regions of the chart. If you are looking at a chart pair (X-bar and R, X-bar and s, or X and MR), look at both charts.

Points falling outside the control limits may be the result of a special cause that was corrected quickly, either intentionally or unintentionally. It may also point to an intermittent problem. The chart below shows two points outside the control limits.

See also:
>> Analyze for special causes of variation
>> Any point lying outside the control limits
>> 7 or more points in a row above or below the center line
>> 7 or more points in one direction
>> Any nonrandom pattern

Comply with critical quality standards, reduce variability, improve profitability, and reduce costs.

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