Certified Six Sigma Black Belt Exam Certified Six Sigma Black Belt Trivia 1 — Questions and Answers
Question 1: What is the term for the ratio of the specification width to the process spread, used to measure process capability?
- Process Sigma
- Cp Index (Correct answer)
- Defects Per Million Opportunities
- Rolled Throughput Yield
Correct answer: Cp Index
The Cp index (process capability index) measures the ratio of the specification width (USL - LSL) to the process spread (6σ), indicating how well a process fits within its specification limits without regard to centering.
Question 2: In a control chart, what does the term 'common cause variation' describe?
- Variation from special events such as equipment failures
- Variation inherent to the process operating normally (Correct answer)
- Variation caused by measurement system error only
- Variation introduced during the Improve phase
Correct answer: Variation inherent to the process operating normally
Common cause variation (also called natural or random variation) is the inherent, predictable variation present in any stable process. It is distinguished from special cause variation, which arises from assignable, non-routine sources.
Question 3: Which Six Sigma metric accounts for the cumulative probability that all process steps produce defect-free output?
- Defects Per Unit (DPU)
- Sigma Level
- Rolled Throughput Yield (RTY) (Correct answer)
- Process Capability Ratio (Cpk)
Correct answer: Rolled Throughput Yield (RTY)
Rolled Throughput Yield (RTY) is calculated by multiplying the first-pass yield of each process step together. It reveals the true probability that a unit passes through all steps without any defects or rework.
Question 4: In hypothesis testing, what is the consequence of committing a Type II error?
- Rejecting a true null hypothesis
- Failing to detect a real effect that exists (Correct answer)
- Setting the alpha level too high
- Using a two-tailed test when one-tailed is appropriate
Correct answer: Failing to detect a real effect that exists
A Type II error (beta error) occurs when the null hypothesis is not rejected even though it is actually false — meaning a real effect or difference goes undetected. This is distinct from a Type I error, which is incorrectly rejecting a true null hypothesis.
Question 5: What is the primary objective of a Gauge Repeatability and Reproducibility (Gauge R&R) study?
- To identify the root cause of process defects
- To quantify the amount of variation contributed by the measurement system (Correct answer)
- To establish control limits for a new control chart
- To validate that a process is in statistical control
Correct answer: To quantify the amount of variation contributed by the measurement system
A Gauge R&R study evaluates how much of the total observed variation is attributable to the measurement system itself (repeatability = same operator, same gauge; reproducibility = different operators). This ensures the measurement system is adequate before analyzing process data.
Question 6: In the DMAIC framework, during which phase would a Black Belt typically apply Statistical Process Control (SPC) charts to sustain improvements?
- Define
- Measure
- Analyze
- Control (Correct answer)
Correct answer: Control
SPC charts are implemented in the Control phase to monitor the improved process over time, detect shifts or trends, and ensure gains achieved during the Improve phase are maintained. The Control phase locks in improvements through monitoring plans and standardized procedures.
Certified Six Sigma Black Belt Exam Certified Six Sigma Black Belt Trivia 1
What is the term for the ratio of the specification width to the process spread, used to measure process capability?