Lean Six Sigma Green Belt Certification Lean Six Sigma Green Belt DMAIC: Improve and Control 1 — Questions and Answers
Question 1: During the Improve phase, a team wants to test multiple input variables simultaneously to determine which combination produces the best output. Which statistical technique is best suited for this?
- Failure Mode and Effects Analysis (FMEA)
- Design of Experiments (DOE) (Correct answer)
- Statistical Process Control (SPC)
- Regression Analysis
Correct answer: Design of Experiments (DOE)
Design of Experiments (DOE) allows teams to systematically test multiple input variables and their interactions simultaneously, making it the most efficient method for finding optimal process settings in the Improve phase.
Question 2: In the Control phase, a process owner notices the X-bar chart shows a single point beyond the upper control limit. According to standard control chart rules, this is an indication of:
- Common cause variation that should be ignored
- A special cause variation requiring investigation (Correct answer)
- Normal process behavior within acceptable limits
- A signal to widen the control limits
Correct answer: A special cause variation requiring investigation
A single point beyond a control limit is one of the standard Western Electric rules for detecting special cause variation, which requires immediate investigation to identify and eliminate the assignable cause.
Question 3: A Lean Six Sigma team has completed the Improve phase and is transitioning to Control. Which document formally assigns ongoing monitoring responsibilities to specific process owners?
- Project Charter
- SIPOC Diagram
- Control Plan (Correct answer)
- Value Stream Map
Correct answer: Control Plan
The control plan is the primary document in the Control phase that defines what to monitor, how to monitor it, measurement frequency, and who is responsible, ensuring the gains from the Improve phase are sustained.
Question 4: When using a Poka-Yoke (mistake-proofing) device as an improvement solution, the primary goal is to:
- Detect defects after they occur so they can be logged
- Make it impossible or immediately obvious when an error is about to happen (Correct answer)
- Train operators to perform inspections more carefully
- Reduce cycle time by eliminating non-value-added steps
Correct answer: Make it impossible or immediately obvious when an error is about to happen
Poka-Yoke devices are designed to either prevent errors from occurring in the first place (prevention type) or detect them the moment they occur (detection type), eliminating reliance on human vigilance.
Question 5: After implementing process improvements, a team wants to confirm the new process mean is statistically different from the old baseline mean. Which statistical test should they use?
- Chi-Square Test
- Two-Sample t-Test (Correct answer)
- F-Test
- Kruskal-Wallis Test
Correct answer: Two-Sample t-Test
A two-sample t-test compares the means of two independent groups (before and after improvement) to determine whether the difference is statistically significant, validating that the improvement had a real effect.
Question 6: In the Control phase, a team decides to use a process behavior chart with subgroups of n=5 collected every hour. What type of chart pair should they use?
- p-chart and np-chart
- c-chart and u-chart
- X-bar and R chart (Correct answer)
- I-MR chart
Correct answer: X-bar and R chart
The X-bar and R chart pair is used for continuous data collected in rational subgroups (typically n=2 to 10), where the X-bar chart monitors the subgroup mean and the R chart monitors subgroup range to detect shifts and spread changes.
Lean Six Sigma Green Belt Certification Lean Six Sigma Green Belt DMAIC: Improve and Control 1
During the Improve phase, a team wants to test multiple input variables simultaneously to determine which combination produces the best output.
Which statistical technique is best suited for this?