Quality Advisor℠

Your proof of quality® resource

4 of 5 beyond 1 sigma

Note: Use this test for control sparingly. There is a tendency to overcontrol the system when using this test. Use it only when there is some doubt about the system’s stability.

When four out of five consecutive points lie beyond the 1-sigma limit on one side of the average, the system is declared unstable.

4 of 5 beyond 1 sigma - chart example

See also:
>> Any nonrandom pattern
>> Too close to the average
>> Too far from the average
>> Cycles
>> Trends
>> Sawtooth
>> Clusters
>> 2 of 3 points beyond 2 sigma

Free monthly quality tips

FREE Newsletter on training tips, statistical help, book reviews and new product informationSubscribe to our free monthly newsletter, Quality eLine. It offers quality improvement information, quality training tips, statistical process control help, gage R&R information, and more.

Subscribe

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

Learn more   Try it!