Lean Six Sigma Green Belt Certification DMAIC: Analyze Phase Techniques 4 — Questions and Answers
Question 1: A process has a cycle time with a right-skewed distribution. Which central tendency measure best represents the typical cycle time for reporting purposes?
- Mean
- Median (Correct answer)
- Mode
- Range
Correct answer: Median
The median is resistant to the pull of extreme high values in right-skewed distributions, making it a better measure of typical performance than the mean.
Question 2: Which tool specifically helps a team distinguish between common cause variation and special cause variation during the Analyze phase?
- Pareto chart
- Control chart (SPC) (Correct answer)
- Histogram
- Scatter diagram
Correct answer: Control chart (SPC)
Control charts use statistical control limits to distinguish between random common cause variation and non-random special cause signals.
Question 3: A team performs a two-sample t-test comparing mean output before and after a process change and obtains p = 0.12 with α = 0.05. What action is recommended?
- Declare the change effective and proceed to Improve
- Fail to reject the null hypothesis; the difference is not statistically significant (Correct answer)
- Reject the null hypothesis since p < 0.20
- Permanently implement the process change
Correct answer: Fail to reject the null hypothesis; the difference is not statistically significant
Since p = 0.12 > α = 0.05, there is insufficient evidence to conclude the means differ; the null hypothesis of no difference is not rejected.
Question 4: What does it mean when a regression model's residuals show a pattern (e.g., funnel shape) when plotted against fitted values?
- The model has a high R² value
- Heteroscedasticity exists, violating regression assumptions (Correct answer)
- The regression is non-significant
- The data is normally distributed
Correct answer: Heteroscedasticity exists, violating regression assumptions
A funnel-shaped residual plot indicates heteroscedasticity (non-constant variance), which violates an assumption of ordinary least squares regression.
Question 5: During an Analyze phase, a value stream map is used primarily to:
- Calculate process sigma level
- Identify non-value-added steps, wait times, and waste in the flow (Correct answer)
- Measure gauge repeatability and reproducibility
- Determine control limits for a process
Correct answer: Identify non-value-added steps, wait times, and waste in the flow
Value stream mapping visually depicts material and information flow to highlight non-value-added activities, wait times, and opportunities for waste elimination.
Question 6: A Green Belt is analyzing data and finds that the X variable explains very little of the variation in Y. The scatter plot shows random scatter. What is the MOST likely conclusion?
- The X variable is the primary root cause
- The X variable has little to no linear relationship with Y (Correct answer)
- More data collection will always reveal a strong relationship
- The regression model should be used for prediction
Correct answer: The X variable has little to no linear relationship with Y
Random scatter with low R² indicates the X variable does not linearly explain Y's variation, suggesting it is not a key process input variable for this outcome.
Question 7: In a cause-and-effect matrix, which inputs receive the highest priority for further investigation?
- Inputs with the lowest frequency of occurrence
- Inputs with the highest weighted score based on correlation to key outputs (Correct answer)
- Inputs listed first on the SIPOC diagram
- Inputs controlled by operators rather than management
Correct answer: Inputs with the highest weighted score based on correlation to key outputs
A cause-and-effect matrix prioritizes inputs by multiplying their correlation ratings to each output by the output's importance weight, then summing across outputs.
Lean Six Sigma Green Belt Certification DMAIC: Analyze Phase Techniques 4
A process has a cycle time with a right-skewed distribution.
Which central tendency measure best represents the typical cycle time for reporting purposes?