Question

Describe how control charts are used to assess process variation.

Answer 1

Control chart is given above on the basis of this control chart we can assess process solution as following type:-

here a single point outside the control limits. In Figure above point sixteen is above the UCL (upper control limit).
Two out of three successive points are on the same side of the centerline and farther than 2 σ from it. In Figure , point 4 sends that signal.
Four out of five successive points are on the same side of the centerline and farther than 1 σ from it. In Figure , point 11 sends that signal.
A run of eight in a row are on the same side of the centerline. Or 10 out of 11, 12 out of 14, or 16 out of 20. In Figure ,point 21 is eighth in a row above the centerline.
Obvious consistent or persistent patterns that suggest something unusual about data and process.

In this way we can draw a conclusion whether the process variation is consistent (in control) or is unpredictable (out of control, affected by special causes of variation).

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