Lean Six Sigma Green Belt Certification DMAIC: Improve and Control 4 — Questions and Answers
Question 1: Which metric best quantifies the long-term process capability when the process mean is not centered between specification limits?
- Cp
- Cpk
- Pp
- Ppk (Correct answer)
Correct answer: Ppk
Ppk measures long-term process performance accounting for both the actual process spread and how far the mean is from the nearest specification limit.
Question 2: A team wants to reduce setup time on a manufacturing line. Which Lean technique specifically targets the reduction of changeover time?
- Kanban
- SMED (Single-Minute Exchange of Die) (Correct answer)
- Andon
- Heijunka
Correct answer: SMED (Single-Minute Exchange of Die)
SMED is a systematic approach to reduce changeover time by converting internal setup steps (done while the machine is stopped) to external steps (done while it runs).
Question 3: What is the key difference between corrective action and preventive action in a control plan?
- Corrective action addresses the measurement system; preventive action addresses the process
- Corrective action responds to an out-of-control event; preventive action eliminates potential causes before they occur (Correct answer)
- Corrective action is documented; preventive action is informal
- Corrective action applies to attribute data; preventive action applies to variable data
Correct answer: Corrective action responds to an out-of-control event; preventive action eliminates potential causes before they occur
Corrective action is reactive, taken after a defect or special cause is detected, while preventive action is proactive, removing the root cause of a potential failure before it materializes.
Question 4: A process has a Cpk of 0.85. What does this indicate?
- The process is highly capable and centered
- The process is capable but not centered within specifications
- The process is producing defects and is not fully capable (Correct answer)
- The process has too little data to assess capability
Correct answer: The process is producing defects and is not fully capable
A Cpk below 1.0 indicates the process is producing output outside the specification limits and is not yet capable of meeting customer requirements.
Question 5: During an experiment, a team notices that temperature and pressure consistently change together across runs. This is an example of which experimental design problem?
- Replication error
- Blocking
- Aliasing
- Confounding due to lurking variable (Correct answer)
Correct answer: Confounding due to lurking variable
When two variables move together unintentionally across experimental runs, their effects become entangled, making it impossible to attribute results to either factor independently.
Question 6: A team uses an EWMA (Exponentially Weighted Moving Average) control chart instead of a Shewhart X-bar chart. What is the primary advantage?
- EWMA requires fewer data points to set control limits
- EWMA is more sensitive to small, sustained process shifts (Correct answer)
- EWMA eliminates the need for rational subgrouping
- EWMA automatically adjusts for seasonal variation
Correct answer: EWMA is more sensitive to small, sustained process shifts
EWMA gives more weight to recent observations and accumulates information over time, making it better at detecting small persistent shifts that a Shewhart chart might miss.
Question 7: At project closure, the Green Belt should confirm financial benefits with which function before reporting them to leadership?
- The project sponsor
- The finance or accounting department (Correct answer)
- The Master Black Belt
- The process owner
Correct answer: The finance or accounting department
Financial benefits must be validated by Finance or Accounting to ensure they are recognized on the income statement or balance sheet and reported accurately to leadership.
Lean Six Sigma Green Belt Certification DMAIC: Improve and Control 4
Which metric best quantifies the long-term process capability when the process mean is not centered between specification limits?