Lean Six Sigma Black Belt Certification Assessment 4 — Questions and Answers
Question 1: A team is assessing a transactional process and wants to quantify how much time is spent on value-added versus non-value-added activities. Which metric is most appropriate?
- Process cycle efficiency (PCE) (Correct answer)
- Takt time
- Defects per unit (DPU)
- Overall equipment effectiveness (OEE)
Correct answer: Process cycle efficiency (PCE)
Process cycle efficiency = Value-Added Time / Total Lead Time, and in lean transactional processes it is typically well below 10%, indicating significant waste.
Question 2: During an attribute agreement analysis, an appraiser's within-appraiser agreement is 100% but their agreement with the standard (known truth) is only 60%. This indicates:
- The appraiser is consistent but inaccurate—a systematic bias exists (Correct answer)
- The measurement system is acceptable for production use
- The appraiser needs more training to improve consistency
- The reference standard itself is unreliable
Correct answer: The appraiser is consistent but inaccurate—a systematic bias exists
High within-appraiser agreement with low accuracy means the appraiser is consistently making the same wrong classification—a systematic error, not random variation.
Question 3: Which statistical test is most appropriate to assess whether a process mean has shifted between two time periods using continuous data that is normally distributed?
- Two-sample t-test (Correct answer)
- Chi-square test
- Mann-Whitney U test
- F-test
Correct answer: Two-sample t-test
The two-sample t-test compares the means of two independent, normally distributed populations to determine if a statistically significant shift has occurred.
Question 4: A Black Belt discovers that the control chart used for baseline assessment had subgroup sizes of 1. Which chart type should have been used?
- Individuals and Moving Range (I-MR) chart (Correct answer)
- X-bar and R chart
- p-chart
- c-chart
Correct answer: Individuals and Moving Range (I-MR) chart
When subgroup size is 1 (individual measurements), the I-MR chart is used, tracking individual values and the moving range between consecutive points.
Question 5: In a process capability assessment, the short-term capability (Cp) is 2.0. Assuming the standard 1.5 sigma process drift, what is the expected long-term DPMO?
- 3.4 DPMO (Correct answer)
- 233 DPMO
- 6,210 DPMO
- 66,807 DPMO
Correct answer: 3.4 DPMO
A short-term Cp of 2.0 corresponds to a 6-sigma process; accounting for the 1.5-sigma long-term shift yields a long-term sigma level of 4.5, which equates to approximately 3.4 DPMO.
Question 6: During a Measure phase tollgate, the project sponsor asks why the team collected 30 subgroups of 5 for the baseline Xbar-R chart. The Black Belt explains this is because:
- 30 subgroups provide sufficient data to detect process patterns and establish reliable control limits (Correct answer)
- AIAG mandates exactly 30 subgroups for all control chart studies
- Fewer subgroups would cause the control limits to be too wide to detect any shifts
- 30 subgroups reduce the risk of Type II errors to below 5%
Correct answer: 30 subgroups provide sufficient data to detect process patterns and establish reliable control limits
Industry convention recommends at least 25–30 subgroups to calculate stable, representative control limits and to identify trends or patterns in baseline data.
Question 7: A team performing a supplier assessment uses DPMO to compare two suppliers. Supplier A has DPMO = 6,210 and Supplier B has DPMO = 66,807. What sigma levels do these represent respectively?
- 4.5 sigma and 3.0 sigma (Correct answer)
- 5.0 sigma and 3.5 sigma
- 4.0 sigma and 2.5 sigma
- 3.5 sigma and 2.0 sigma
Correct answer: 4.5 sigma and 3.0 sigma
6,210 DPMO corresponds to a 4.5 sigma process (short-term 6σ with 1.5σ shift) and 66,807 DPMO corresponds to a 3.0 sigma process level.
Lean Six Sigma Black Belt Certification Assessment 4
A team is assessing a transactional process and wants to quantify how much time is spent on value-added versus non-value-added activities.
Which metric is most appropriate?