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Why do we need a validation set and a test set?

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We split the data into three different categories while creating a model:

Training set: We use the training set for building the model and adjusting the model’s variables. But, we cannot rely on the correctness of the model build on top of the training set. The model might give incorrect outputs on feeding new inputs.

Validation set: We use a validation set to look into the model’s response on top of the samples that don’t exist in the training dataset. Then, we will tune hyperparameters on the basis of the estimated benchmark of the validation data.

When we are evaluating the model’s response using the validation set, we are indirectly training the model with the validation set. This may lead to the overfitting of the model to specific data. So, this model won’t be strong enough to give the desired response to the real-world data.

Test set: The test dataset is the subset of the actual dataset, which is not yet used to train the model. The model is unaware of this dataset. So, by using the test dataset, we can compute the response of the created model on hidden data. We evaluate the model’s performance on the basis of the test dataset.

Note: We always expose the model to the test dataset after tuning the hyperparameters on top of the validation set.

As we know, the evaluation of the model on the basis of the validation set would not be enough. Thus, we use a test set for computing the efficiency of the model.

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