Lean Six Sigma Green Belt Certification Measure Phase and Statistics 4 — Questions and Answers
Question 1: A normal distribution has 99.73% of data within how many standard deviations of the mean?
- 1
- 2
- 3 (Correct answer)
- 6
Correct answer: 3
The empirical rule states that 99.73% of data falls within ±3 standard deviations of the mean in a normal distribution.
Question 2: What does the acronym DPMO stand for in Six Sigma?
- Defects Per Million Opportunities (Correct answer)
- Defective Parts Measured Optimally
- Data Points Mapped to Output
- Defects Per Manufacturing Operation
Correct answer: Defects Per Million Opportunities
DPMO stands for Defects Per Million Opportunities and is the standard metric used to calculate sigma level.
Question 3: In a Gage R&R study expressed as %Study Variation, what threshold is typically considered acceptable for measurement systems?
- Less than 10% (Correct answer)
- Less than 30%
- Less than 50%
- Less than 70%
Correct answer: Less than 10%
A %Study Variation below 10% indicates an acceptable measurement system; 10-30% may be acceptable depending on context.
Question 4: Which distribution is most appropriate for modeling the number of defects per unit when defects are rare and independent?
- Normal distribution
- Binomial distribution
- Poisson distribution (Correct answer)
- Exponential distribution
Correct answer: Poisson distribution
The Poisson distribution models the number of rare, independent events occurring in a fixed interval of time or space.
Question 5: What is the difference between accuracy and precision in measurement systems?
- Accuracy is about repeatability; precision is about bias
- Accuracy is closeness to true value; precision is consistency of repeated measurements (Correct answer)
- Accuracy measures resolution; precision measures discrimination
- They are interchangeable terms in Six Sigma
Correct answer: Accuracy is closeness to true value; precision is consistency of repeated measurements
Accuracy refers to how close a measurement is to the true value (low bias), while precision refers to how consistently measurements repeat.
Question 6: A process with Cp = 1.5 but Cpk = 0.8 indicates:
- The process is capable and well-centered
- The process has adequate spread but is significantly off-center (Correct answer)
- The process spread exceeds specifications
- Both indices are acceptable
Correct answer: The process has adequate spread but is significantly off-center
Cp measures potential capability based on spread alone; when Cpk is much lower, the process is not centered between specification limits.
Question 7: Which continuous probability distribution is symmetric, bell-shaped, and fully described by its mean and variance?
- Exponential
- Weibull
- Normal (Correct answer)
- Uniform
Correct answer: Normal
The normal (Gaussian) distribution is symmetric and bell-shaped, completely defined by its mean (μ) and variance (σ²).
Lean Six Sigma Green Belt Certification Measure Phase and Statistics 4
A normal distribution has 99.73% of data within how many standard deviations of the mean?