Lean Six Sigma Green Belt Certification Control Phase and Sustainment 5 — Questions and Answers
Question 1: What is the MAIN risk of setting control limits too wide on an X-bar chart?
- The chart will generate too many false alarms
- Real process shifts may not be detected until many defects are produced (Correct answer)
- Operators will adjust the process too frequently
- The subgroup sample size will need to increase
Correct answer: Real process shifts may not be detected until many defects are produced
Overly wide control limits reduce the chart's sensitivity, meaning actual process deterioration may go undetected for an extended period, increasing defect output.
Question 2: Which metric is MOST appropriate for tracking long-term process capability in the Control phase?
- Pp (process performance index)
- Cpk (process capability index) (Correct answer)
- Sigma level based on short-term DPMO
- Average defect rate from the Measure phase baseline
Correct answer: Cpk (process capability index)
Cpk measures ongoing process capability relative to specifications while accounting for process centering, making it the standard metric for monitoring sustained capability.
Question 3: An I-MR chart is used instead of an X-bar and R chart when:
- The process has multiple streams that need simultaneous monitoring
- Only one measurement per time period is practical or available (Correct answer)
- The data is attribute (pass/fail) rather than continuous
- The subgroup size exceeds 10 units
Correct answer: Only one measurement per time period is practical or available
Individuals and Moving Range (I-MR) charts are designed for situations where subgroup sampling is not feasible and only a single observation is available per time period.
Question 4: A project benefit realization review is typically conducted to:
- Determine if the Green Belt should receive certification
- Confirm that the financial savings projected during the project were actually achieved (Correct answer)
- Decide whether to apply the project approach to other areas
- Evaluate the quality of the control plan documentation
Correct answer: Confirm that the financial savings projected during the project were actually achieved
A benefit realization review validates that the anticipated financial and operational benefits (savings, quality improvements) actually occurred after project implementation.
Question 5: In a control plan, the 'reaction plan' column is triggered when:
- A new operator joins the team and needs training
- A measurement exceeds the control limit or action threshold (Correct answer)
- The process capability falls below Cpk 1.33 during an annual review
- An audit identifies a documentation gap in the SOP
Correct answer: A measurement exceeds the control limit or action threshold
The reaction plan activates when a control measurement signals an out-of-control or out-of-specification condition, providing a predefined escalation and correction sequence.
Question 6: Which of the following best describes a 'holding the gains' strategy in Lean Six Sigma?
- Locking specification limits so they cannot be changed by engineering
- Using a combination of SOPs, control charts, audits, and training to prevent regression to the old process (Correct answer)
- Freezing the process from any future improvement activity
- Requiring management sign-off before any process parameter is adjusted
Correct answer: Using a combination of SOPs, control charts, audits, and training to prevent regression to the old process
Holding the gains uses multiple overlapping controls — documentation, monitoring, training, and periodic audits — to prevent natural organizational drift back to old habits.
Question 7: When transferring a completed DMAIC project to the process owner, the handoff package should EXCLUDE:
- Updated control plan with reaction plans
- All raw data and statistical analyses from every phase (Correct answer)
- Revised SOPs and operator training materials
- The project charter and financial validation sign-off
Correct answer: All raw data and statistical analyses from every phase
The handoff package should include actionable control documents and context, but voluminous raw phase data is typically archived rather than transferred since it is not needed for day-to-day process management.
Lean Six Sigma Green Belt Certification Control Phase and Sustainment 5
What is the MAIN risk of setting control limits too wide on an X-bar chart?