juniorModel Evaluation
What is data leakage in model evaluation?
Updated May 17, 2026
Short answer
Data leakage occurs when test information influences training.
Deep explanation
It leads to overly optimistic performance because the model indirectly learns from test data.
Real-world example
Including future sales data when predicting past demand.
Common mistakes
- Fitting preprocessing on full dataset before splitting.
Follow-up questions
- How to prevent leakage?
- What is target leakage?