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

Question

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Special causes indicate that the process is not in a state of statistical control, and therefore the data generated is not representative of the true process. Including such data in the calculations of center line and control limits will lead to biased values, which would not provide an accurate representation of the process.

In Developing Process Control Charts, If Special Causes Are Present