Lean Six Sigma Green Belt Certification Control Phase and Sustainment 3 — Questions and Answers
Question 1: After project closure, responsibility for sustaining process improvements typically transfers to:
- The Green Belt who led the project
- The process owner or operations manager (Correct answer)
- The Master Black Belt who coached the project
- The finance department that validated savings
Correct answer: The process owner or operations manager
The process owner or operations manager assumes accountability for sustaining improvements after the project team disbands, ensuring long-term ownership.
Question 2: Which tool BEST helps identify which process inputs require monitoring in the Control phase?
- Affinity diagram
- Control-Impact matrix
- Cause-and-effect matrix (C&E matrix)
- FMEA with Risk Priority Numbers (Correct answer)
Correct answer: FMEA with Risk Priority Numbers
The FMEA with Risk Priority Numbers (RPNs) prioritizes which failure modes and inputs pose the highest risk, directing control plan monitoring efforts to the most critical variables.
Question 3: What is the difference between common cause variation and special cause variation?
- Common cause is controllable; special cause is not
- Common cause is inherent to the system; special cause comes from assignable external factors (Correct answer)
- Common cause requires immediate investigation; special cause does not
- Common cause only occurs in manufacturing; special cause occurs in services
Correct answer: Common cause is inherent to the system; special cause comes from assignable external factors
Common cause variation is the natural, inherent variation within a stable system, while special cause variation results from identifiable, assignable factors outside the system.
Question 4: A Green Belt wants to verify the measurement system is still adequate before finalizing the control plan. Which study should be conducted?
- Process capability study
- Gage R&R study (Correct answer)
- Hypothesis test
- Regression analysis
Correct answer: Gage R&R study
A Gage R&R (Repeatability and Reproducibility) study evaluates whether the measurement system has acceptable precision relative to process variation and tolerances.
Question 5: In a control plan, 'frequency' refers to:
- How often the process is allowed to go out of control
- How often a measurement is taken for a given CTQ or control variable (Correct answer)
- The number of defects per million opportunities
- The sampling rate used to build the control chart baseline
Correct answer: How often a measurement is taken for a given CTQ or control variable
Frequency in a control plan specifies how often each characteristic must be measured (e.g., every hour, every 50 units) to detect shifts in the process in a timely manner.
Question 6: Which of the following signals on an X-bar chart requires immediate investigation according to standard SPC rules?
- Two points near the centerline on alternating sides
- One point beyond 3 sigma control limits (Correct answer)
- Six points alternating up and down
- Four points between 1 and 2 sigma on one side
Correct answer: One point beyond 3 sigma control limits
A single point beyond the 3-sigma control limits is the most fundamental out-of-control signal indicating a likely special cause that requires immediate investigation.
Question 7: Mistake-proofing (poka-yoke) devices are preferred in the Control phase because they:
- Require extensive statistical training to implement
- Prevent errors from occurring rather than detecting them after the fact (Correct answer)
- Replace the need for operator training entirely
- Are less expensive than control charts to implement
Correct answer: Prevent errors from occurring rather than detecting them after the fact
Poka-yoke devices are preferred because they prevent defects from being produced or passed forward, making them more effective than detection-based controls.
Lean Six Sigma Green Belt Certification Control Phase and Sustainment 3
After project closure, responsibility for sustaining process improvements typically transfers to: