Lean Six Sigma Yellow Belt Certification The Analyze Phase 4 — Questions and Answers
Question 1: What is the difference between 'common cause' and 'special cause' variation?
- Common cause is controllable; special cause is not
- Common cause is inherent to the process; special cause is due to specific, assignable factors (Correct answer)
- Special cause variation is always larger than common cause
- Common cause requires immediate corrective action
Correct answer: Common cause is inherent to the process; special cause is due to specific, assignable factors
Common cause variation is the normal, random variation within a stable process, while special cause variation results from specific, identifiable factors outside the normal system.
Question 2: Which of the following is an example of non-value-added but necessary (NVAN) work?
- Reworking a defective product
- Waiting for a machine to warm up
- Regulatory compliance reporting required by law (Correct answer)
- Searching for misplaced tools
Correct answer: Regulatory compliance reporting required by law
NVAN activities do not add value from the customer's perspective but are required due to regulatory, legal, or business constraints.
Question 3: A team maps their process and finds steps where partially finished work sits idle awaiting the next operation. Which type of waste does this represent?
- Overproduction
- Waiting
- Motion
- Inventory (Correct answer)
Correct answer: Inventory
Inventory waste (also called 'work in progress' or WIP) occurs when partially finished goods or services accumulate between process steps.
Question 4: During the Analyze phase, a team uses a box plot. What does the line inside the box represent?
- The mean of the dataset
- The median (50th percentile) (Correct answer)
- The upper control limit
- The standard deviation
Correct answer: The median (50th percentile)
In a box plot, the line inside the box represents the median, which divides the dataset so that half the values fall above and half below.
Question 5: Which Six Sigma concept measures the number of standard deviations between the process mean and the nearest specification limit?
- Cp index
- Sigma level (Z-score) (Correct answer)
- Range (R)
- Coefficient of variation
Correct answer: Sigma level (Z-score)
The sigma level (or Z-score) measures how many standard deviations the process mean is from the specification limit, indicating process capability.
Question 6: What is the primary goal of a root cause analysis in the Analyze phase?
- To document the problem for stakeholders
- To identify and verify the true cause driving the problem, not just its symptoms (Correct answer)
- To calculate the financial impact of defects
- To assign responsibility for quality failures
Correct answer: To identify and verify the true cause driving the problem, not just its symptoms
Root cause analysis aims to identify the fundamental cause of a problem so that solutions address the source rather than temporary symptoms.
Question 7: A process improvement team finds that most defects occur during the last hour of the work shift. Which analytical approach would best confirm this finding?
- Run a regression analysis on all data
- Stratify defect data by time of day or shift segment (Correct answer)
- Create a SIPOC diagram for the last hour
- Calculate the overall process Cpk
Correct answer: Stratify defect data by time of day or shift segment
Stratifying defect data by time period allows the team to confirm whether defect rates truly differ across shift segments and quantify the difference.
Lean Six Sigma Yellow Belt Certification The Analyze Phase 4
What is the difference between 'common cause' and 'special cause' variation?