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Rule of Seven Tests The tests state that an out of control situation is present if one of the following conditions is true: 1) Seven points in a row above the average, 2) Seven points in a row below the average, 3) Seven points in a row trending up, or 4) Seven points in a row trending down.

All control charts have three basic components: a centerline, usually the mathematical average of all the samples plotted. upper and lower statistical control limits that define the constraints of common cause variations. performance data plotted over time.

A process is said to be out of control if: One or more data points fall outside the control limits. Seven consecutive data points increasing or decreasing. Eight consecutive data points are on one side of average. Fourteen consecutive data points alternating up & down.

In general, the chart contains a center line that represents the mean value for the in-control process. Two other horizontal lines, called the upper control limit (UCL) and the lower control limit (LCL), are also shown on the chart.

A process is said to be in control when the control chart does not indicate any out-of-control condition and contains only common causes of variation. If the common cause variation is small, then a control chart can be used to monitor the process.

Points Beyond the Control Limits Action should be taken to find the special cause and permanently remove it from the process. If there is a point beyond the control limits, there is no need to apply the other tests for out of control situations.

Nelson rules RuleDescriptionProblem IndicatedRule 8Eight points in a row exist, but none within 1 standard deviation of the mean, and the points are in both directions from the mean.Jumping from above to below while missing the first standard deviation band is rarely random.7 more rows

The following rules can be used to properly interpret control charts: Rule 1 ? One point beyond the 3 ? control limit. Rule 2 ? Eight or more points on one side of the centerline without crossing. Rule 3 ? Four out of five points in zone B or beyond. Rule 4 ? Six points or more in a row steadily increasing or decreasing.

Basic Procedure Determine the appropriate time period for collecting and plotting data. Collect data, construct your chart and analyze the data. Look for "out-of-control signals" on the control chart. When one is identified, mark it on the chart and investigate the cause.

How do I know if my process is in-control? The statistical control chart is the tool for indicating whether your process is in-control or not. If your data points are falling within the calculated control limits and are random, that's an indication that your process is in-control.