Lean Six Sigma Yellow Belt Certification Lean Six Sigma Yellow Belt Root Cause Analysis 1 — Questions and Answers
Question 1: In the DMAIC methodology, during which phase is Root Cause Analysis primarily performed?
- Define
- Measure
- Analyze (Correct answer)
- Improve
Correct answer: Analyze
Root Cause Analysis belongs in the Analyze phase, where teams examine collected data and use tools like fishbone diagrams and 5 Whys to identify the fundamental causes of defects before moving to solutions.
Question 2: What is the primary purpose of a Pareto chart when used in root cause analysis?
- To display process steps in sequence
- To identify the vital few causes responsible for the majority of defects (Correct answer)
- To track individual measurements over time
- To show the correlation between two variables
Correct answer: To identify the vital few causes responsible for the majority of defects
A Pareto chart applies the 80/20 rule, visually separating the 'vital few' causes (roughly 20%) that drive most problems (roughly 80%) from the 'trivial many,' helping teams prioritize where to focus RCA efforts.
Question 3: In a fishbone (Ishikawa) diagram, what do the diagonal 'bones' branching from the main spine represent?
- Individual defect occurrences
- Potential cause categories (Correct answer)
- Corrective action steps
- Process measurement points
Correct answer: Potential cause categories
The diagonal bones represent major cause categories (such as the 6Ms: Man, Machine, Method, Material, Measurement, Mother Nature). Sub-causes are then listed as smaller branches within each category.
Question 4: Which root cause analysis tool is best suited for visually determining whether a relationship exists between two process variables?
- Histogram
- Scatter diagram (Correct answer)
- Affinity diagram
- SIPOC map
Correct answer: Scatter diagram
A scatter diagram plots pairs of data points for two variables on X and Y axes, making it possible to see whether a positive, negative, or no correlation exists — helping teams validate suspected cause-and-effect relationships.
Question 5: When applying the 5 Whys technique, what signals that you have reached a true root cause?
- You have asked 'why' exactly five times
- The answer points to an actionable process or system failure you can fix (Correct answer)
- The team unanimously agrees on the answer
- The answer involves a measurement value
Correct answer: The answer points to an actionable process or system failure you can fix
The goal of 5 Whys is not to ask exactly five questions but to keep digging until you reach an actionable root cause — typically a process, system, or policy failure — where a countermeasure can be applied to prevent recurrence.
Question 6: What is the key distinction between a 'symptom' and a 'root cause' in problem-solving?
- A symptom is always quantifiable; a root cause is not
- A symptom is the observable evidence of a problem; a root cause is the fundamental reason the problem occurs (Correct answer)
- A symptom always appears after the root cause is identified
- A symptom and a root cause describe the same event from different perspectives
Correct answer: A symptom is the observable evidence of a problem; a root cause is the fundamental reason the problem occurs
A symptom is the visible or measurable effect (e.g., increased defects), while the root cause is the underlying systemic reason that, if eliminated, prevents the symptom from recurring. Treating only symptoms leads to temporary fixes.
Lean Six Sigma Yellow Belt Certification Lean Six Sigma Yellow Belt Root Cause Analysis 1
In the DMAIC methodology, during which phase is Root Cause Analysis primarily performed?