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December 29, 2025 · 1 min read

What is a training set validation set and test set — and why do you need all three?

Training set is used to fit the model. Validation set is used to tune hyperparameters and select the best model. Test set is held out completely and used only once…

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SOFTWARE_ARCHITECT // AI_ENGINEER

📅 Dec 29, 2025 ⏱ 1 min read

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What is a training set validation set and test set — and why do you need all three?

COVER // WHAT IS A TRAINING SET VALIDATION SET AND TEST SET — AND WHY DO YOU NEED ALL THREE?

Training set is used to fit the model. Validation set is used to tune hyperparameters and select the best model. Test set is held out completely and used only once to report final performance. Using only train/test leads to overfitting on the test set through repeated evaluation.

beginner evaluation ml train-test-split validation

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