Lean Six Sigma Green Belt Certification Measure Phase and Statistics 2 — Questions and Answers
Question 1: A process has a mean of 50 and a standard deviation of 5. What is the coefficient of variation (CV)?
- 5%
- 10% (Correct answer)
- 25%
- 50%
Correct answer: 10%
CV = (standard deviation / mean) × 100 = (5/50) × 100 = 10%.
Question 2: Which measurement scale allows calculation of meaningful ratios between values?
- Nominal
- Ordinal
- Interval
- Ratio (Correct answer)
Correct answer: Ratio
Ratio scales have a true zero point, allowing meaningful ratio comparisons such as 'twice as much.'
Question 3: In a Gage R&R study, if reproducibility is very high relative to total variation, what is the most likely cause?
- The measurement equipment is worn out
- Different operators measure the same part differently (Correct answer)
- Parts are too similar to distinguish
- The study sample size is too small
Correct answer: Different operators measure the same part differently
High reproducibility variation indicates operator-to-operator differences are contributing significantly to measurement variation.
Question 4: A control chart shows a run of 8 consecutive points on one side of the centerline. This is an example of:
- Random variation
- A special cause signal (Correct answer)
- Acceptable common cause variation
- Measurement system error
Correct answer: A special cause signal
Eight or more consecutive points on the same side of the centerline is a standard Western Electric rule indicating a non-random special cause.
Question 5: What does kurtosis measure in a data distribution?
- The center of the distribution
- The spread of the distribution
- The asymmetry of the distribution
- The peakedness and tail heaviness of the distribution (Correct answer)
Correct answer: The peakedness and tail heaviness of the distribution
Kurtosis measures how peaked or flat a distribution is relative to a normal distribution, and the weight of its tails.
Question 6: Which sampling method divides a population into subgroups and randomly samples from each subgroup proportionally?
- Simple random sampling
- Systematic sampling
- Stratified sampling (Correct answer)
- Cluster sampling
Correct answer: Stratified sampling
Stratified sampling ensures representation from all key subgroups by sampling proportionally from each stratum.
Question 7: A process produces 25 defective units out of 500 total units. What is the defect rate in parts per million (PPM)?
- 25,000
- 50,000 (Correct answer)
- 500
- 5,000
Correct answer: 50,000
PPM = (defects / total units) × 1,000,000 = (25/500) × 1,000,000 = 50,000 PPM.
Lean Six Sigma Green Belt Certification Measure Phase and Statistics 2
A process has a mean of 50 and a standard deviation of 5.
What is the coefficient of variation (CV)?