Certified Six Sigma Black Belt Exam Certified Six Sigma Black Belt Statistical Process Control (SPC) Questions and Answers 2

Question 1

A Six Sigma Black Belt notices that all plotted points on an X-bar chart fall within the control limits but seven consecutive points are above the center line. What should be concluded?

Accepted Answer

A special cause of variation is likely present

Answer

Seven or more consecutive points on one side of the center line indicate a run, which is evidence of a special cause of variation even though no points exceed the control limits.

Question 2

Which control chart is most appropriate for monitoring the number of paint defects found on each automobile body when the inspection area varies from vehicle to vehicle?

Accepted Answer

u chart

Answer

The u chart monitors the number of defects per unit of measure and is used when the area of opportunity (inspection area) is not constant across samples.

Question 3

When calculating the process capability index Cpk, a Black Belt obtains Cpk = 1.0 and Cp = 1.5. What does this indicate about the process?

Accepted Answer

The process is capable but not centered within the specification limits

Answer

A Cp of 1.5 shows the process spread fits well within the specifications, but a lower Cpk of 1.0 reveals the process mean has shifted away from the center of the specification range.

Question 4

An EWMA chart is preferred over a Shewhart X-bar chart in which of the following situations?

Accepted Answer

When detecting small sustained shifts in the process mean

Answer

The EWMA (Exponentially Weighted Moving Average) chart is specifically designed to detect small, sustained shifts in the process mean by incorporating weighted historical data into each plotted point.

Question 5

A process has a Pp of 1.33 but a Cp of 0.89. What is the most likely explanation?

Accepted Answer

The process has significant between-subgroup variation that inflates overall variability

Answer

A Pp greater than Cp is unusual; however, when Cp is lower than Pp it typically indicates the within-subgroup estimate of sigma is larger, but here Pp > Cp means long-term sigma is smaller, which suggests the subgrouping strategy may not be capturing the true short-term variation correctly.

Certified Six Sigma Black Belt Exam Practice Test

Certified Six Sigma Black Belt Exam Practice Test

Certified Six Sigma Black Belt Exam Certified Six Sigma Black Belt Statistical Process Control (SPC) Questions and Answers 2