2026-04-16 11:31 Tags:
🧠 1. What is Gini impurity (intuition)?
👉 Gini impurity measures:
“How mixed a group is”
Think like this:
You randomly pick one sample from a group.
👉 Gini = probability that you misclassify it
Examples
Case 1: perfectly pure
[Fraud, Fraud, Fraud, Fraud]👉 Gini = 0
✔️ no confusion
✔️ perfect
Case 2: very mixed
[Fraud, Legit, Fraud, Legit]👉 Gini = high (~0.5)
❌ very confusing
👉 So:
| Situation | Gini |
|---|---|
| pure | 0 |
| mixed | high |
🔢 2. The formula
We want to minimize the gini impurity in the leaf node