Figure 3:

σ² vs. ID regression for 6 variance models on the Zhou and Ren’s circular tunnel dataset. As shown, the quadratic-variance model (Model #4 in Table 1) accounts for 84.4% of variance in the observed variance of MT. It performs the best according to AIC, WAIC, and leave-one-(A, W)-out cross-validation. The R² value of Model #6 in Table 1 is the same with Model #4, but Model #6 overfits the data because it has higher RMSE in leave-one-(A, W)-out cross-validation compared with quadratic variance model.