Single Decision Tree — Instability
Each resample draws 30 points with replacement.
The decision boundary lurches — high variance!
Ensemble Error vs Number of Trees B
B =
1
Test Error at B trees:
0.200
Var(ensemble) = σ²/B
σ² = 0.04 (single tree variance)
At B=1: error = 0.200 | At B=100: error ≈ 0.020
Variance shrinks 100× with 100 trees.