Lean Six Sigma Green Belt Certification DMAIC: Measure Phase Tools 3 — Questions and Answers
Question 1: A team calculates Pp = 1.45 and Ppk = 0.92 for a new process. What is the most likely explanation?
- The process is centered and capable
- The process has adequate spread but is significantly off-center (Correct answer)
- The process has too much variation to be useful
- Pp and Ppk cannot differ by this amount
Correct answer: The process has adequate spread but is significantly off-center
When Pp is acceptable but Ppk is low, it means the process spread is adequate but the mean is shifted away from the target, reducing Ppk.
Question 2: What is the defects per million opportunities (DPMO) for a process operating at 4 sigma?
- 3.4
- 6,210 (Correct answer)
- 66,807
- 308,537
Correct answer: 6,210
A 4-sigma process corresponds to approximately 6,210 DPMO when using the standard Six Sigma convention that assumes a 1.5-sigma shift.
Question 3: In a control chart, which pattern would NOT trigger a Western Electric (WE) rule violation?
- One point beyond 3 sigma
- Six consecutive points steadily increasing
- Four of five points beyond 1 sigma on one side
- Alternate points zig-zagging above and below the centerline within 1 sigma (Correct answer)
Correct answer: Alternate points zig-zagging above and below the centerline within 1 sigma
Alternating zig-zag points within 1 sigma of the centerline is a common cause pattern and does not trigger any Western Electric rule.
Question 4: What does the 'discrimination ratio' in a gauge R&R study tell practitioners?
- How many distinct categories the gauge can reliably distinguish in the data (Correct answer)
- The percentage of variation due to the gauge
- The ratio of appraisers to parts measured
- How accurate the gauge is versus a master standard
Correct answer: How many distinct categories the gauge can reliably distinguish in the data
The discrimination ratio (also called number of distinct categories, NDC) indicates how many statistically distinct groups the measurement system can differentiate in the process variation.
Question 5: A practitioner uses stratified sampling by shift (day, evening, night) and takes equal samples from each. This approach ensures:
- Every unit has an equal chance regardless of shift
- Representation from each subgroup is guaranteed (Correct answer)
- Only the highest-volume shift is represented
- Samples are collected in a fixed time interval
Correct answer: Representation from each subgroup is guaranteed
Stratified sampling divides the population into subgroups (strata) and samples from each, ensuring all groups are represented in the dataset.
Question 6: Which tool would best help a Green Belt identify the input variables most likely to affect a key output metric before detailed data collection?
- Control chart
- Cause-and-effect (fishbone) diagram (Correct answer)
- Gauge R&R study
- Box plot
Correct answer: Cause-and-effect (fishbone) diagram
A cause-and-effect diagram (Ishikawa/fishbone) systematically brainstorms potential input variables across categories such as people, methods, machines, materials, and environment.
Question 7: A spaghetti diagram is most useful in the Measure phase for:
- Plotting defect rates over time
- Visualizing physical movement of people or materials in a process (Correct answer)
- Comparing the distribution of two groups
- Identifying statistical outliers
Correct answer: Visualizing physical movement of people or materials in a process
A spaghetti diagram traces the actual physical path of people, materials, or information through a workspace, revealing waste in motion and transportation.
Lean Six Sigma Green Belt Certification DMAIC: Measure Phase Tools 3
A team calculates Pp = 1.45 and Ppk = 0.92 for a new process.
What is the most likely explanation?