Certified Six Sigma Black Belt Exam FREE Certified Six Sigma Black Belt Statistical Process Control (SPC) Questions and Answers 2 — Questions and Answers
Question 1: A process has a Cp of 1.33 and a Cpk of 0.89. What does this indicate?
- The process is capable but not centered within the specification limits (Correct answer)
- The process is both capable and centered
- The process is neither capable nor centered
- The specification limits are too narrow
Correct answer: The process is capable but not centered within the specification limits
When Cp exceeds Cpk, it indicates the process has adequate spread relative to specifications but the mean has shifted away from the center of the tolerance band.
Question 2: Which control chart is most appropriate for monitoring the number of paint defects found on each automobile body panel when the inspection area varies by panel size?
- u-chart (Correct answer)
- c-chart
- np-chart
- p-chart
Correct answer: u-chart
The u-chart tracks defects per unit of measure, making it appropriate when the sample size or area of opportunity varies between subgroups.
Question 3: On an X-bar and R chart, what is the primary purpose of rational subgrouping?
- To maximize variation within subgroups and minimize variation between subgroups
- To ensure subgroups are randomly selected from the entire production run
- To group data so that special cause variation appears between subgroups rather than within them (Correct answer)
- To guarantee equal sample sizes across all subgroups
Correct answer: To group data so that special cause variation appears between subgroups rather than within them
Rational subgrouping arranges data so that common cause variation is captured within subgroups, causing any special cause variation to show up as differences between subgroup averages.
Question 4: A process is in statistical control but producing 4% nonconforming output. What is the correct course of action?
- Adjust the process whenever a defective unit is detected
- Implement fundamental process changes to reduce common cause variation (Correct answer)
- Add more control chart rules to detect shifts earlier
- Tighten the control limits on the existing chart
Correct answer: Implement fundamental process changes to reduce common cause variation
A stable process producing unacceptable defect levels requires management action to change the system and reduce common cause variation, not tampering or tighter chart limits.
Question 5: What does the Western Electric Rule for 2 out of 3 consecutive points beyond 2 sigma indicate on a control chart?
- A run pattern suggesting a trend
- A potential small shift in the process mean (Correct answer)
- Random variation within expected limits
- A definitive out-of-control condition requiring process shutdown
Correct answer: A potential small shift in the process mean
The 2-of-3 beyond 2-sigma rule is a sensitizing rule designed to detect small sustained shifts in the process mean that a single point beyond 3-sigma might miss.
Question 6: When calculating control limits for an X-bar chart with subgroup size n=5, which factor is used to estimate the process standard deviation from the average range?
- d2 (Correct answer)
- A2
- D4
- E2
Correct answer: d2
The d2 factor converts the average range to an estimate of the process standard deviation using the formula σ̂ = R̄/d2, and its value depends on the subgroup size.
Certified Six Sigma Black Belt Exam FREE Certified Six Sigma Black Belt Statistical Process Control (SPC) Questions and Answers 2
A process has a Cp of 1.33 and a Cpk of 0.89.
What does this indicate?