Certified Six Sigma Black Belt Exam Basic 5 — Questions and Answers
Question 1: The 'Control' phase of DMAIC primarily uses which tool to sustain improvements after project completion?
- Value stream mapping
- Control plan and control charts (Correct answer)
- Regression analysis
- Hypothesis testing
Correct answer: Control plan and control charts
A control plan documents the monitoring approach, and control charts provide ongoing statistical signals to maintain process gains after the project is closed.
Question 2: What is 'sigma shift' and why is it used in Six Sigma calculations?
- A 1.5-sigma adjustment added to account for long-term process drift (Correct answer)
- The shift from defect measurement to opportunity measurement
- The conversion factor between DPMO and percent yield
- A correction applied when sample sizes are small
Correct answer: A 1.5-sigma adjustment added to account for long-term process drift
A 1.5-sigma shift is added to short-term sigma calculations to account for typical long-term process drift and mean shifts, making the DPMO tables more realistic.
Question 3: Which of the following is an example of a 'common cause' variation in a process?
- A machine tool breaking mid-production
- Random fluctuations inherent to the process operating normally (Correct answer)
- A new untrained operator making errors
- Raw material from a defective supplier batch
Correct answer: Random fluctuations inherent to the process operating normally
Common cause variation is the natural, inherent random variation always present in a stable process — it can only be reduced by changing the process system.
Question 4: What statistical tool is used to quantify the strength and direction of the linear relationship between two continuous variables?
- Chi-square test of independence
- Pearson correlation coefficient (Correct answer)
- F-test of variance equality
- Kruskal-Wallis test
Correct answer: Pearson correlation coefficient
The Pearson correlation coefficient (r) ranges from -1 to +1 and measures both the strength and direction of the linear relationship between two continuous variables.
Question 5: In the context of Six Sigma project selection, a 'Business Case' should include:
- Detailed statistical analysis of the root causes
- The financial impact and strategic alignment of the project (Correct answer)
- A complete list of potential solutions
- The training plan for the project team members
Correct answer: The financial impact and strategic alignment of the project
A Business Case articulates why the project matters by linking it to financial impact, cost of poor quality, and strategic business objectives to justify resources.
Question 6: Which sampling strategy ensures every member of the population has an equal chance of being selected?
- Stratified sampling
- Systematic sampling
- Simple random sampling (Correct answer)
- Cluster sampling
Correct answer: Simple random sampling
Simple random sampling gives every unit in the population an equal and independent chance of being selected, minimizing selection bias.
Question 7: A Black Belt notices that a control chart shows 8 consecutive points on one side of the centerline. This pattern indicates:
- The process is operating normally within control limits
- A special cause has shifted the process mean (Correct answer)
- The control limits need to be recalculated
- The measurement system has high variation
Correct answer: A special cause has shifted the process mean
Eight or more consecutive points on the same side of the centerline is a Western Electric run rule violation, signaling a likely process mean shift due to a special cause.
Certified Six Sigma Black Belt Exam Basic 5
The 'Control' phase of DMAIC primarily uses which tool to sustain improvements after project completion?