Lean Six Sigma Green Belt Certification LSSGB 1 — Questions and Answers
Question 1: When a data point falls outside the control limits on an X-bar control chart, this most likely indicates:
- The process is incapable and must be redesigned
- A special cause of variation has entered the process (Correct answer)
- The sample size used for subgrouping is too small
- Common cause variation is higher than expected
Correct answer: A special cause of variation has entered the process
Points outside control limits signal special (assignable) cause variation — an unusual event or shift not inherent to the process. Common cause variation, by definition, keeps points within the limits. The correct response is to investigate and eliminate the special cause before drawing conclusions about capability.
Question 2: In Lean, 'takt time' is defined as:
- The average cycle time measured across all workstations
- The available production time divided by customer demand rate (Correct answer)
- The total lead time from raw material receipt to shipment
- The time a unit waits between consecutive process steps
Correct answer: The available production time divided by customer demand rate
Takt time (from German 'beat') sets the production pace required to meet customer demand. It is calculated as Available Production Time ÷ Customer Demand. It serves as the heartbeat that synchronizes process output to pull — not a measure of actual cycle time or lead time.
Question 3: Which of the following is NOT one of the eight wastes in Lean manufacturing (DOWNTIME)?
- Non-utilized talent
- Overproduction
- Inspection (Correct answer)
- Transportation
Correct answer: Inspection
The 8 Lean wastes (DOWNTIME) are: Defects, Overproduction, Waiting, Non-utilized talent, Transportation, Inventory, Motion, and Extra-processing. Inspection is not a standalone named waste — though it may be a symptom of defects or over-processing, it does not appear as one of the eight categories.
Question 4: In a Gauge R&R (Measurement System Analysis) study, 'Reproducibility' specifically quantifies:
- Variation attributed to the measurement instrument itself when used by one operator
- Variation that arises when different operators measure the same part with the same gauge (Correct answer)
- Variation due to differences between the parts sampled for the study
- The combined measurement system variation as a percentage of total process variation
Correct answer: Variation that arises when different operators measure the same part with the same gauge
Reproducibility captures operator-to-operator variation — how consistently different people obtain the same reading on the same part with the same instrument. Repeatability, by contrast, is instrument variation from a single operator. Distinguishing the two guides whether to address the tool or the people/training.
Question 5: In inferential statistics, what is the correct interpretation when a Six Sigma team rejects the null hypothesis?
- The alternative hypothesis has been proven with absolute certainty
- The sample data provides sufficient evidence that the null hypothesis is unlikely to be true (Correct answer)
- The p-value exceeded the chosen significance level (alpha)
- The process has been confirmed to be in statistical control
Correct answer: The sample data provides sufficient evidence that the null hypothesis is unlikely to be true
Rejecting the null hypothesis means the observed data would be very unlikely if H₀ were true (p ≤ alpha), so the team concludes there is sufficient statistical evidence against it. It does not 'prove' the alternative — it simply means H₀ is implausible given the data. Rejection occurs when p ≤ alpha, not p > alpha.
Question 6: In Failure Mode and Effects Analysis (FMEA), the Risk Priority Number (RPN) is calculated by multiplying:
- Severity, Occurrence, and Detection (Correct answer)
- Probability, Impact, and Urgency
- Frequency, Criticality, and Controllability
- Severity, Likelihood, and Exposure
Correct answer: Severity, Occurrence, and Detection
RPN = Severity × Occurrence × Detection. Each factor is rated on a 1–10 scale. Severity measures impact if the failure occurs, Occurrence measures how frequently it might happen, and Detection measures how likely the current controls are to catch the failure before it reaches the customer. Higher RPN scores prioritize remediation efforts.
Lean Six Sigma Green Belt Certification LSSGB 1
When a data point falls outside the control limits on an X-bar control chart, this most likely indicates: