Lean Six Sigma Yellow Belt Certification The Control Phase 2 — Questions and Answers
Question 1: What is the primary purpose of a control chart in the Control phase?
- To identify root causes of defects
- To monitor process performance over time and detect special cause variation (Correct answer)
- To calculate the process capability index
- To document standard operating procedures
Correct answer: To monitor process performance over time and detect special cause variation
Control charts monitor process performance over time, distinguishing between common cause and special cause variation.
Question 2: Which of the following best describes 'common cause variation'?
- Variation caused by a specific identifiable event
- Variation that signals a process is out of control
- Natural, inherent variation present in every process (Correct answer)
- Variation that requires immediate corrective action
Correct answer: Natural, inherent variation present in every process
Common cause variation is the natural, random variation inherent in a stable process and does not require special intervention.
Question 3: A control plan is created during the Control phase. What is its main function?
- To outline the project charter and scope
- To document how the process improvements will be sustained over time (Correct answer)
- To identify potential failure modes before they occur
- To map the current-state value stream
Correct answer: To document how the process improvements will be sustained over time
A control plan documents the methods, responsibilities, and monitoring activities needed to sustain process improvements.
Question 4: In a control chart, what does a data point outside the upper or lower control limit indicate?
- Common cause variation
- A process that is perfectly centered
- Special cause variation requiring investigation (Correct answer)
- That the specification limits need adjustment
Correct answer: Special cause variation requiring investigation
A point outside control limits signals special cause variation, indicating an unusual event that should be investigated.
Question 5: What does 'mistake-proofing' (poka-yoke) aim to achieve in the Control phase?
- Reducing cycle time by eliminating non-value-added steps
- Preventing defects by making errors impossible or immediately detectable (Correct answer)
- Training employees to work faster and more efficiently
- Measuring process capability on a regular schedule
Correct answer: Preventing defects by making errors impossible or immediately detectable
Poka-yoke devices or methods prevent errors from occurring or detect them immediately so they cannot become defects.
Question 6: Which metric is most commonly used to measure process capability in the Control phase?
- Takt time
- Cp or Cpk (Correct answer)
- Net Promoter Score
- Rolled throughput yield
Correct answer: Cp or Cpk
Cp and Cpk measure how well a process fits within its specification limits relative to its natural variation.
Question 7: What is the recommended response when a control chart signals a special cause?
- Widen the control limits to accommodate the variation
- Ignore it if the data point is close to the limit
- Investigate the cause and take corrective action (Correct answer)
- Recalculate the process average and continue
Correct answer: Investigate the cause and take corrective action
Special cause signals require investigation to identify and eliminate the root cause to prevent recurrence.
Lean Six Sigma Yellow Belt Certification The Control Phase 2
What is the primary purpose of a control chart in the Control phase?