TL;DR Resaon Example affect Model’s complexity ⬆️ Model’s complexity ⬇️ Bias wrong assumption assume a quadratic model to be linear underfitting ⬇️ ⬆️ Variance excessive sensitivity to small variations high-degree polynomial model overfitting ⬆️ ⬇️ Inreducible error noisy data Explaination A model’s generalization error can be expressed as the sum of three very different errors: