Module 4 · Lesson 1 of 22
Analyze-phase strategy and evidence hierarchy
This lesson and the entire Lean Six Sigma Black Belt academy are free of charge — no fees, ever.
Learning objectives
- State the intent of Analyze in one sentence.
- Sequence process-door and data-door evidence.
- Set an evidence hierarchy for cause claims.
What Analyze must deliver
Analyze converts hypotheses into confirmed root causes. Every cause must be observable, testable and controllable before it becomes a candidate for Improve.
The evidence hierarchy runs from anecdote → stratified data → statistical test → replicated experiment or removal/reappearance evidence.
Garment-factory example
A puckering hypothesis is downgraded from ‘folder alignment’ (anecdote) to ‘folder alignment on fabric construction X above speed Y’ once stratified data and a small test confirm the mechanism.
Method
- Restate the Y and known baseline.
- List candidate Xs with source (process-door or data-door).
- Plan tests that could disprove each cause.
- Rank surviving Xs by strength of evidence.
Common mistakes
- Skipping to solutions before causes are confirmed.
- Accepting seniority as evidence.
Knowledge check
Pick one answer per question. Explanations appear after you submit.
1. A root cause must be:
2. In the evidence hierarchy, replicated experiment ranks:
Author: NOSK.life · Last reviewed: 2026-07-21