Quality Advisor

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

7 points in a row above or below the centerline

To apply this test, look for groups of points above or below the average or centerline. Count consecutive points. Are there groups of seven or more? This is probably the result of a shift in one of the system resources (materials, people, methods, environment, information aids, equipment, and measurement). The following chart, which can be created using SQCpack, shows two groups, one with eight above the centerline and one with seven below.

7 points in a row above or below the centerline - sample chart

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

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