Lean Six Sigma Green Belt Certification Prep 5 — Questions and Answers
Question 1: What is the purpose of a 'Poka-Yoke' device in Lean Six Sigma?
- To track cycle time across workstations
- To mistake-proof a process and prevent defects from occurring or escaping (Correct answer)
- To visualize workflow on a kanban board
- To measure gauge repeatability
Correct answer: To mistake-proof a process and prevent defects from occurring or escaping
Poka-Yoke (Japanese for 'mistake-proofing') devices are designed to prevent errors from occurring or to detect them immediately so they cannot reach the next step.
Question 2: A team is comparing average delivery times between three different shipping carriers. Which statistical test is most appropriate?
- Two-sample t-test
- Paired t-test
- One-way ANOVA (Correct answer)
- Chi-square test
Correct answer: One-way ANOVA
One-way ANOVA is used to compare means across three or more groups simultaneously while controlling the risk of Type I error inflation.
Question 3: In a Value Stream Map (VSM), what does a 'push' arrow indicate?
- Material flows based on actual customer demand
- Material is pushed to the next step based on a schedule or forecast regardless of need (Correct answer)
- Information flows electronically
- A supermarket pull system is in place
Correct answer: Material is pushed to the next step based on a schedule or forecast regardless of need
A push arrow in VSM indicates that material is moved forward based on production schedules or forecasts, not actual downstream demand — a common source of overproduction waste.
Question 4: What does 'Sigma shift' of 1.5 account for in Six Sigma calculations?
- Measurement system error in gauge studies
- Long-term process drift and shift that occurs over time (Correct answer)
- The difference between DPMO and DPU
- Confidence intervals in hypothesis testing
Correct answer: Long-term process drift and shift that occurs over time
The 1.5 sigma shift acknowledges that real processes drift over time, so short-term capability is adjusted to predict long-term performance (e.g., a 6-sigma short-term process yields 3.4 DPMO long-term).
Question 5: Which tool is most appropriate for identifying potential failure modes and their effects before a process is launched?
- Control chart
- FMEA (Failure Mode and Effects Analysis) (Correct answer)
- Gauge R&R study
- Regression analysis
Correct answer: FMEA (Failure Mode and Effects Analysis)
FMEA proactively identifies potential failures, their effects, and their causes, then prioritizes them by Risk Priority Number (RPN) to focus prevention efforts.
Question 6: What is the key distinction between 'common cause' and 'special cause' variation?
- Common cause variation is large; special cause variation is small
- Common cause is inherent to the process; special cause comes from assignable factors outside normal operation (Correct answer)
- Common cause requires immediate action; special cause can be tolerated
- They are different names for the same phenomenon
Correct answer: Common cause is inherent to the process; special cause comes from assignable factors outside normal operation
Common cause variation is random noise built into the system, while special cause variation results from specific identifiable factors that fall outside the normal process.
Question 7: A Green Belt notices that the Xbar-R control chart for a machining process shows the R chart is in control but the Xbar chart has several points outside control limits. What should be concluded?
- Both charts must be out of control for any action to be taken
- The process variation is stable but the process average has shifted — investigate mean shifts (Correct answer)
- The measurement system needs recalibration
- The subgroup size is too small to draw conclusions
Correct answer: The process variation is stable but the process average has shifted — investigate mean shifts
An in-control R chart with an out-of-control Xbar chart means variability is consistent but the process mean is experiencing shifts — a classic indicator of process setting changes.
Lean Six Sigma Green Belt Certification Prep 5
What is the purpose of a 'Poka-Yoke' device in Lean Six Sigma?