Data leakage occurs when evaluation information influences model choices, making validation or test performance look better than performance on genuinely new data. section 5.2.1
Repeated validation tuning
Try a configuration, evaluate it on the validation set, and change the model based on the score. Repeating this process leaks increasing information about the validation data and can overfit the configuration to it. section 5.2.1
Use separate evaluation roles:
- Tune model configuration with training and validation data, recognizing that repeated validation feedback becomes a form of learning. section 5.2.1
- Reserve the test set as a completely different, never-before-seen dataset. section 5.2.1
- Use hold-out validation, K-fold validation, or iterated K-fold validation when data is limited. section 5.2.1








