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.
