Absolute error (AE) measures a regression residual as |y − f(x)|, the absolute difference between the target and prediction. It corresponds to assuming a Laplacian distribution over residuals. section 7.3.1
Use absolute error to understand these practical tradeoffs:
- Penalizes large errors less aggressively than squared error, making it less sensitive to outliers. section 7.3.1
- Lacks second-order differentiability, so it cannot be used directly with Newton boosting. section 7.3.1
- Contrasts with Huber loss, which uses squared error for small residuals and scaled absolute error beyond a threshold. section 7.3.1
Figure 7.10 Loss and log-likelihood functions for three different types of targets: continuous-valued (left), positive continuous-valued (center), and count-valued (right)
Compare the absolute-error curve with squared error and other loss functions across residual sizes. section 7.3.1

