Certified Six Sigma Black Belt Exam Process Capability Analysis

Question 1

What does the Cp index measure in process capability analysis?

Accepted Answer

Process spread relative to specification width

Answer

Cp = (USL - LSL) / (6σ) measures the ratio of the specification width to the process spread, indicating potential capability regardless of centering.

Question 2

A process has Cp = 1.5 and Cpk = 0.8. What does this indicate?

Accepted Answer

The process has sufficient spread but is significantly off-center

Answer

Cp = 1.5 indicates sufficient process spread potential, but Cpk = 0.8 (below 1.0) reveals the process mean is significantly shifted away from the specification center.

Question 3

What is the standard minimum acceptable Cpk value for a process to be considered 'capable' in most Six Sigma guidelines?

Accepted Answer

1.33

Answer

A Cpk of 1.33 corresponds to a 4-sigma process producing approximately 64 DPMO and is the widely accepted minimum threshold for process capability.

Question 4

Which capability index accounts for BOTH process spread AND centering simultaneously?

Accepted Answer

Cpk

Answer

Cpk = min[(USL − μ)/3σ, (μ − LSL)/3σ] takes the minimum of both one-sided indices, penalizing any shift of the mean toward either specification limit.

Question 5

What is the key difference between Cpk and Ppk?

Accepted Answer

Cpk uses within-subgroup (short-term) variation; Ppk uses total (long-term) variation

Answer

Cpk uses within-subgroup standard deviation (short-term, potential capability), while Ppk uses overall standard deviation from all data (long-term, actual performance).

Certified Six Sigma Black Belt Exam Practice Test

Certified Six Sigma Black Belt Exam Practice Test

Certified Six Sigma Black Belt Exam Process Capability Analysis