## 9.5 Resampling methods (4): Leave-one-out cross-validation (LOOCV)

• Q: James et al. (2013) use Figure 5.3 [p.179] to explain the Leave-One-Out Cross-Validation (LOOCV). Please inspect the figure and explain it in a few words.

• Data set repeatedly split into two parts, whereby a single observation $$(x_{1},y_{1})$$ is used for validation set
• Remaining observations $${(x_{2},y_{2}),...,(x_{n},y_{n})}$$ make up the training set
• Statistical learning method is fit on the $$n−1$$ training observations and prediction is made for excluded observation
• Repeated for all splits