Which of the following is true regarding the process capability index Cpk?
A) A Cpk index value of 1 is ideal, meaning all units meet specifications.
B) The larger the Cpk, the more units meet specifications.
C) The Cpk index can only be used when the process centerline is also the specification centerline.
D) Positive values of the Cpk index are good; negative values are bad.
E) None of the above is true.

Question

Quizplus · Accepted Answer

Option A is incorrect because a Cpk index value of 1 is not ideal, it only means that the process is capable of meeting the specifications.
Option C is incorrect because the process centerline and specification centerline can be different, but this can affect the calculation of the Cpk index.
Option D is incorrect because negative values of the Cpk index indicate that the process is not capable of meeting the specification and requires improvement; but a very high positive value of Cpk is also not always desirable as it indicates that the process variability is very low and it may lead to other problems.
Therefore, option B is correct because a higher value of the Cpk index indicates more units meeting the specifications and better process capability.

Which of the Following Is True Regarding the Process Capability