Which of the following conceptual definitions of the Cpk capability index is most accurate?
A) The quantity of the upper customer specification minus the lower specification divided by six sigma.
B) The quantity of the upper customer specification minus the lower specification divided by three sigma.
C)The smallest of the quantity of process mean minus the lower customer specification divided by three sigma or the quantity of the upper customer specification minus the process mean divided by three sigma.
D)The difference between the upper customer specification and the upper control limit plus the difference between the lower customer specification and the lower control limit.

Question

Which of the following conceptual definitions of the Cpk capability index is most accurate?
A) The quantity of the upper customer specification minus the lower specification divided by six sigma.
B) The quantity of the upper customer specification minus the lower specification divided by three sigma. 
C)The smallest of the quantity of process mean minus the lower customer specification divided by three sigma or the quantity of the upper customer specification minus the process mean divided by three sigma.
D)The difference between the upper customer specification and the upper control limit plus the difference between the lower customer specification and the lower control limit.

Quizplus · Accepted Answer

Cpk is a measure of process capability which shows how well a process is meeting specifications. It is calculated as the minimum of two ratios: one that measures how close the process mean is to the lower specification limit (LSL), and another that measures how close the process mean is to the upper specification limit (USL), both normalized by the process variability (3 sigma). This is accurately described in option C.

Which of the Following Conceptual Definitions of the Cpk Capability