Lean Six Sigma Green Belt Certification Certified Six Sigma Green Belt 1 — Questions and Answers
Question 1: What distinguishes common cause variation from special cause variation in a process?
- Common cause variation is inherent and systemic to the process, while special cause variation stems from assignable, external factors (Correct answer)
- Common cause variation requires immediate corrective action, while special cause variation can be ignored
- Common cause variation is always larger in magnitude than special cause variation
- Common cause variation only occurs in manufacturing processes, while special cause variation occurs in service processes
Correct answer: Common cause variation is inherent and systemic to the process, while special cause variation stems from assignable, external factors
Common cause (or random) variation is the natural, built-in noise of a stable process and can only be reduced by changing the system itself. Special cause variation is triggered by identifiable, assignable factors outside the normal process and requires targeted investigation and removal.
Question 2: In a simple linear regression model, what does the coefficient of determination (R²) represent?
- The slope of the best-fit regression line relating X to Y
- The proportion of total variance in the response variable that is explained by the predictor variable (Correct answer)
- The p-value indicating whether the regression relationship is statistically significant
- The standard error of the residuals around the regression line
Correct answer: The proportion of total variance in the response variable that is explained by the predictor variable
R² ranges from 0 to 1 and quantifies how much of the variability in Y is accounted for by its linear relationship with X. An R² of 0.85, for example, means 85% of Y's variation is explained by the model, leaving 15% unexplained.
Question 3: What is the primary purpose of conducting a Gage Repeatability and Reproducibility (Gage R&R) study?
- To calculate the process capability index (Cpk) for a critical-to-quality characteristic
- To quantify how much of the observed process variation is attributable to the measurement system itself (Correct answer)
- To identify which operators are performing below standard and require retraining
- To establish the upper and lower specification limits for a product characteristic
Correct answer: To quantify how much of the observed process variation is attributable to the measurement system itself
A Gage R&R study partitions total observed variation into process variation and measurement system variation (repeatability = equipment variation, reproducibility = appraiser-to-appraiser variation). If the measurement system contributes too large a share, the data used for decisions is unreliable.
Question 4: Which of the following best describes a key deliverable of the Measure phase in DMAIC?
- A prioritized list of verified root causes derived from hypothesis testing
- A baseline process capability or sigma level that quantifies current performance (Correct answer)
- A set of implemented solutions validated through pilot runs
- A control plan with response procedures for out-of-control conditions
Correct answer: A baseline process capability or sigma level that quantifies current performance
The Measure phase establishes a data-driven baseline — capturing how the process performs today before any changes are made. This baseline (often expressed as Cpk, DPMO, or sigma level) becomes the benchmark against which Improve-phase gains are measured.
Question 5: In Design of Experiments (DOE), what is a 'main effect'?
- The combined interaction effect when two or more factors are changed simultaneously
- The average change in the response variable when a single factor moves from its low level to its high level (Correct answer)
- The residual error remaining after all factor effects are accounted for in the model
- The center-point run used to detect curvature in a factorial experiment
Correct answer: The average change in the response variable when a single factor moves from its low level to its high level
A main effect measures the individual impact of one factor on the response, averaged across all levels of the other factors. It is distinct from an interaction effect, which occurs when the effect of one factor depends on the level of another factor.
Question 6: What is the primary purpose of a Pareto chart in a Six Sigma project?
- To determine whether process output follows a normal distribution
- To track a quality metric over time and detect process shifts
- To apply the 80/20 rule by identifying the vital few categories that account for the majority of defects or problems (Correct answer)
- To display the relationship and correlation strength between two continuous variables
Correct answer: To apply the 80/20 rule by identifying the vital few categories that account for the majority of defects or problems
A Pareto chart ranks defect categories by frequency (or cost) in descending order with a cumulative percentage line, making it easy to see which few categories drive most of the problem. Focusing improvement efforts on those 'vital few' typically yields the greatest return.
Lean Six Sigma Green Belt Certification Certified Six Sigma Green Belt 1
What distinguishes common cause variation from special cause variation in a process?