Lean Six Sigma Green Belt Certification Lean Six Sigma Green Belt DMAIC: Measure Phase Tools 1 — Questions and Answers
Question 1: What is the key difference between the Cp and Cpk process capability indices?
- Cp accounts for process centering while Cpk measures only spread
- Cpk accounts for process centering while Cp measures only spread relative to specification width (Correct answer)
- Cp is used for attribute data while Cpk is used for continuous variable data
- Cpk measures long-term capability while Cp measures short-term capability
Correct answer: Cpk accounts for process centering while Cp measures only spread relative to specification width
Cpk incorporates where the process mean sits relative to the specification limits, penalizing processes that are off-center. Cp only compares the process spread to the specification width, ignoring whether the process is centered — so two processes with identical Cp values can have very different Cpk values.
Question 2: In Measurement System Analysis (MSA), what does 'reproducibility' specifically quantify?
- Variation in measurements taken by the same operator on the same part multiple times
- Variation in measurements when different operators measure the same part with the same instrument (Correct answer)
- The total combined error of the measurement instrument
- Variation caused by measuring the same part on different days
Correct answer: Variation in measurements when different operators measure the same part with the same instrument
Reproducibility captures operator-to-operator variation — how much measurements differ when different appraisers measure the same part using the same gauge. Repeatability, by contrast, is the variation seen when one operator repeatedly measures the same part.
Question 3: A process operating at Six Sigma quality level produces how many defects per million opportunities (DPMO)?
- 0.002 DPMO
- 3.4 DPMO (Correct answer)
- 233 DPMO
- 66,807 DPMO
Correct answer: 3.4 DPMO
A Six Sigma process produces no more than 3.4 DPMO. This figure accounts for a 1.5-sigma long-term shift in the process mean that is assumed to occur in real-world processes, making 3.4 DPMO the accepted benchmark for Six Sigma performance.
Question 4: Which control chart is most appropriate for monitoring the mean of a continuous variable when measurements are collected in subgroups of n = 5?
- p-chart
- c-chart
- X-bar and R chart (Correct answer)
- u-chart
Correct answer: X-bar and R chart
The X-bar and R chart is designed for continuous (variable) data collected in rational subgroups, plotting subgroup means on the X-bar chart and subgroup ranges on the R chart. The p-chart, c-chart, and u-chart are all designed for attribute (count or proportion) data.
Question 5: A four-step process has first-time yields of 95%, 92%, 88%, and 90% respectively. What is the Rolled Throughput Yield (RTY)?
- 91.25%
- 69.2% (Correct answer)
- 80.0%
- 75.4%
Correct answer: 69.2%
RTY is calculated by multiplying the first-time yield of each step: 0.95 × 0.92 × 0.88 × 0.90 = 0.6919, approximately 69.2%. RTY exposes hidden rework and scrap that a final-step yield metric alone would conceal, making it a critical Measure phase metric.
Question 6: What is the primary purpose of developing a formal data collection plan at the start of the Measure phase?
- To identify the root cause of the highest-priority defect type
- To ensure data is gathered consistently, completely, and free from collection bias (Correct answer)
- To establish statistical control limits for monitoring the process
- To rank potential improvement solutions by expected impact
Correct answer: To ensure data is gathered consistently, completely, and free from collection bias
A data collection plan defines what to measure, operational definitions, who collects data, sampling strategy, and recording methods before any data is gathered. This structure prevents inconsistent measurement, missing data, and collector bias that would invalidate downstream analysis.
Lean Six Sigma Green Belt Certification Lean Six Sigma Green Belt DMAIC: Measure Phase Tools 1
What is the key difference between the Cp and Cpk process capability indices?