Lean Six Sigma Green Belt Certification Lean Six Sigma Green Belt Knowledge 1 — Questions and Answers
Question 1: Which statistical measure describes the spread of data around the mean by calculating the average of squared deviations?
- Standard deviation
- Variance (Correct answer)
- Range
- Median absolute deviation
Correct answer: Variance
Variance is the average of the squared deviations from the mean. Standard deviation is simply the square root of variance and is more commonly reported, but variance is the direct measure of squared deviations.
Question 2: In the DMAIC framework, during which phase would a team use a Fishbone (Ishikawa) diagram to identify root causes?
- Define
- Measure
- Analyze (Correct answer)
- Improve
Correct answer: Analyze
The Fishbone diagram is a root cause analysis tool used in the Analyze phase to systematically explore potential causes of a defect or problem across categories such as Man, Machine, Method, Material, Measurement, and Environment.
Question 3: What does Process Capability Index (Cpk) measure?
- The total number of defects per million opportunities
- How well a process fits within specification limits, accounting for process centering (Correct answer)
- The ratio of total variation to within-subgroup variation
- The average cycle time of a process step
Correct answer: How well a process fits within specification limits, accounting for process centering
Cpk measures how well a process performs relative to its specification limits while also accounting for whether the process mean is centered. A Cpk of 1.33 or higher is generally considered acceptable.
Question 4: Which of the following best describes 'Poka-Yoke' in Lean manufacturing?
- A visual signal system used to trigger replenishment of materials
- A method for standardizing shift handovers
- A mistake-proofing mechanism that prevents defects from occurring or reaching the next step (Correct answer)
- A technique for balancing workload across operators
Correct answer: A mistake-proofing mechanism that prevents defects from occurring or reaching the next step
Poka-Yoke (mistake-proofing) involves designing processes or tools so that errors are impossible or immediately detected, preventing defects from being passed downstream.
Question 5: A control chart shows several consecutive points trending upward on one side of the center line. This pattern is called:
- Common cause variation
- A run rule violation indicating a special cause (Correct answer)
- Bimodal distribution
- Natural process drift within control limits
Correct answer: A run rule violation indicating a special cause
A run rule violation — such as seven or more consecutive points trending in one direction — signals a special cause of variation. Even if all points remain within control limits, a non-random pattern indicates the process has shifted.
Question 6: In Lean Six Sigma, what is the purpose of a Measurement System Analysis (MSA) / Gauge R&R study?
- To determine the sample size needed for hypothesis testing
- To evaluate whether the measurement system itself contributes significant variation to the data (Correct answer)
- To map the value stream and identify non-value-added steps
- To prioritize root causes using a Pareto chart
Correct answer: To evaluate whether the measurement system itself contributes significant variation to the data
Gauge R&R (Repeatability and Reproducibility) is an MSA technique that quantifies how much of the observed variation in data comes from the measurement system (equipment and operators) versus the actual process, ensuring data quality before analysis.
Lean Six Sigma Green Belt Certification Lean Six Sigma Green Belt Knowledge 1
Which statistical measure describes the spread of data around the mean by calculating the average of squared deviations?