Variation and Root Cause
Analyze-phase root-cause drills cover common and special cause variation, Pareto, fishbone, 5 Whys, FMEA, stratification, scatterplots, and cause validation.
How to study for Six Sigma Green Belt
Use DMAIC as the map: define the problem and customer need, measure the process, analyze causes, improve the system, and control the gains.
Core concepts
Concept 1
Variation and Root Cause questions reward the answer that follows the official source, the professional role, and the stated facts.
Exam cue: Identify the candidate role, client or public risk, source rule, calculation, or process step being tested.
Concept 2
The strongest answer identifies the rule, safety concern, ethical duty, calculation, client factor, or process step before acting.
Exam cue: Check whether the fact pattern is using a national standard, jurisdiction rule, handbook policy, or scenario-specific instruction.
Concept 3
Eliminate answers that ignore requirements, skip documentation, overreach the role, or treat convenience as the standard.
Exam cue: Choose the compliant and professionally scoped answer before the convenient or familiar answer.
Risk pitfalls and guardrails
Treating related standards as interchangeable without checking the source.
Guardrail: Avoid answers that rely only on habit, ignore the stated source, skip safety or compliance steps, or choose convenience over the professional standard.
Skipping screening, documentation, authorization, sanitation, recordkeeping, or other required procedure.
Guardrail: Avoid answers that rely only on habit, ignore the stated source, skip safety or compliance steps, or choose convenience over the professional standard.
Choosing an answer that protects convenience instead of client safety, public protection, or the stated professional duty.
Guardrail: Avoid answers that rely only on habit, ignore the stated source, skip safety or compliance steps, or choose convenience over the professional standard.
Memory anchors
Common Cause
Common cause variation is inherent in the current process system.
Special Cause
Special cause variation comes from an identifiable unusual source.
Pareto
Pareto analysis helps prioritize the vital few categories contributing most to the problem.
Fishbone
A fishbone diagram organizes potential causes by categories.
5 Whys
5 Whys pushes beyond symptoms toward deeper process causes.
Stratification
Stratification separates data into meaningful groups to reveal patterns.
Scatterplot
A scatterplot shows the relationship between two variables.
FMEA
FMEA prioritizes potential failures by severity, occurrence, and detection.
Root Cause
A root cause should be supported by evidence, not only team opinion.
Validation
Cause validation tests whether changing the input changes the output.
Checkpoint rule
Do the check-up only after you can summarize each concept in one sentence and identify one dangerous pitfall from memory.
Knowledge Check (after reading)
Short check-up to confirm understanding of this module.
Check-up Questions
A stable process shows routine fluctuation around its center with no signals. What type of variation is most likely?
A control chart shows a single point far beyond the upper control limit after a machine repair. What should be investigated?
Answer all questions to submit.
Next step personalized recommendations
Continue learning
Move forward only after this module is stable.
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