A manufacturer embarking on a Six Sigma program sets the goal of having True Six Sigma capability for all processes by the end of the month. If their current process capability index on a key metric is less than 2.0 and the process capability ratio is 1.25, what must happen with the process standard deviation?
A) The process standard deviation must be reduced by about 25%.
B) The process standard deviation must be reduced by about 37%.
C) The process standard deviation must be reduced by about 50%.
D) The process standard deviation must be reduced by about 67%.

Question

Quizplus · Accepted Answer

To achieve True Six Sigma capability, the process capability index (Cpk) must be at least 2.0. Currently, the Cpk is less than 2.0 and the process capability ratio (Cp/Cpk) is 1.25, indicating that there is room for improvement. The process standard deviation (sigma) must be reduced to achieve a Cpk of 2.0. The formula for Cpk is (USL-LSL)/(6*sigma), where USL is the upper specification limit, LSL is the lower specification limit, and sigma is the process standard deviation. Therefore, to achieve a Cpk of 2.0, the standard deviation must be reduced by (1.33*sigma)/2, which is about 37%. Therefore, option B is the correct answer.

A Manufacturer Embarking on a Six Sigma Program Sets the Goal