Analyze
The Analyze phase identifies and verifies the root causes that drive the problem. Green Belts combine graphical exploration with basic statistical tests to separate real signals from noise and to confirm which inputs actually influence the output.
Root-cause tools
Fishbone (Ishikawa) diagrams organize potential causes into categories, and the 5 Whys technique drills from a symptom toward an underlying cause. Pareto charts then focus effort on the vital few categories that generate most of the problem.
Hypothesis testing basics
A hypothesis test compares a null hypothesis of no effect against an alternative. When the p-value is below the chosen alpha (often 0.05) the null is rejected. A Type I error is a false positive and a Type II error is failing to detect a real effect.
Correlation and regression
Correlation (r) measures the strength and direction of a linear relationship, while regression models how an output changes with an input. Importantly, a strong correlation shows association, not proof of causation, which must be confirmed experimentally.