Lean Six Sigma Green Belt Certification DMAIC: Improve and Control 2 — Questions and Answers
Question 1: A Green Belt team has identified three potential solutions with similar cost. Which technique best prioritizes them based on impact versus effort?
- Pareto chart
- Pugh concept selection matrix (Correct answer)
- Box plot analysis
- Fishbone diagram
Correct answer: Pugh concept selection matrix
A Pugh concept selection matrix scores competing solutions against weighted criteria such as impact, cost, and feasibility to guide selection.
Question 2: During a pilot run of a new process, the team observes that output variability decreased but the mean shifted away from target. What is the most likely next step?
- Accept the solution since variability improved
- Adjust process settings to re-center the mean while preserving reduced variability (Correct answer)
- Restart DMAIC from the Define phase
- Remove the pilot and revert to the original process
Correct answer: Adjust process settings to re-center the mean while preserving reduced variability
When a pilot reduces variability but shifts the mean, the team should tune the control factors (e.g., setpoints) to re-center output without sacrificing the variability gains.
Question 3: Which type of mistake-proofing device physically prevents a defect from being passed to the next step?
- Detection poka-yoke (Correct answer)
- Warning poka-yoke
- Control poka-yoke
- Prediction poka-yoke
Correct answer: Detection poka-yoke
A detection poka-yoke identifies a defect after it occurs and prevents it from moving forward, while a control (prevention) poka-yoke stops the defect from being made at all.
Question 4: A control chart shows a process in statistical control, but customer complaints persist. What should the team investigate first?
- Recalculate control limits using a larger subgroup size
- Check whether the control chart specifications match customer requirements (Correct answer)
- Switch from an X-bar R chart to an individuals chart
- Increase sampling frequency
Correct answer: Check whether the control chart specifications match customer requirements
A process can be statistically stable yet still fail to meet customer specs if the control limits were set without reference to specification limits.
Question 5: In Design of Experiments, what does 'confounding' mean?
- Two factors are set at the same level across all runs
- The effect of one factor cannot be separated from the effect of another (Correct answer)
- Experimental error exceeds the main effect size
- The center points differ significantly from factorial points
Correct answer: The effect of one factor cannot be separated from the effect of another
Confounding occurs in fractional factorial designs when the effects of two or more factors or interactions are aliased, making it impossible to distinguish their individual contributions.
Question 6: What is the primary purpose of a pre-control chart in the Control phase?
- To replace the control plan after process stabilization
- To provide a simple, specification-based method for operators to detect process shifts (Correct answer)
- To calculate Cpk in real time
- To identify special causes by comparing to historical baselines
Correct answer: To provide a simple, specification-based method for operators to detect process shifts
Pre-control uses zones based on specification limits to give operators a straightforward signal to stop and adjust before defects are produced.
Question 7: A team completes the Improve phase and hands off to operations. Which document is most critical to ensure the improvement is sustained?
- Project charter
- SIPOC diagram
- Control plan (Correct answer)
- Value stream map
Correct answer: Control plan
The control plan documents what to measure, how often, who is responsible, and what actions to take when out-of-control conditions occur, making it the anchor for sustaining improvements.
Lean Six Sigma Green Belt Certification DMAIC: Improve and Control 2
A Green Belt team has identified three potential solutions with similar cost.
Which technique best prioritizes them based on impact versus effort?