In developing process control charts, if special causes are present, they are not representative of true state of statistical control, and the calculations of the center line and control limits will be biased.

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Quizplus · Accepted Answer

This is true. Special causes are attributed to factors outside of the normal process variation, and their presence can indicate a change in the system. The center line and control limits on process control charts are based on the average and variation of the process data, so the presence of special causes can affect these calculations and make them biased or invalid. Therefore, special causes must be identified and investigated separately from the common cause variation in the process in order to achieve statistical control.

In Developing Process Control Charts, If Special Causes Are Present