Data considerations for CUSUM Chart

To ensure that your results are valid, consider the following guidelines when you collect data, perform the analysis, and interpret your results.

The data should be continuous

If your data are counts of defectives or defects, use an attribute control chart, such as P Chart or U Chart.

Small shifts in the data are important

If you do not want to detect small shifts in a process, use a variables chart for subgroups, such as Xbar-R Chart, or an variables chart for individuals, such as I-MR Chart.

The observations within each subgroup should not be correlated with each other

If consecutive data points within each subgroup are correlated, the control limits will be too narrow, and the control chart might incorrectly show some in-control points as out of control.

The data should be in time order

Because control charts detect changes over time, the order of the data is important. You should enter the data in the order it was collected, with the oldest data at the top of the worksheet.

The data should be collected at appropriate time intervals

Collect data at equally spaced time intervals, such as every hour, every shift, or every day. Select a time interval that is short enough that you can identify changes to the process soon after the changes occur.

Data cannot be missing for an entire subgroup

If data for an entire subgroup is missing, Minitab will not create the chart.

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