What Is Cross-Validation In Machine Learning

A dataset must be partitioned into training and validation datasets for cross-validation. The gap between the training and testing or validation datasets may then be calculated. Various forms of cross-validation approaches will divide the primary dataset in multiple ways. The model is often iterated with different training and testing data subtests during the testing stage.

This guide looks into cross-validation in machine learning, covering what it is, why it is required, and examples of cross-validation strategies.


The use of multiple methodologies to test a machine learning model's capacity to generalize while processing new and unknown datasets is cross-validation. Generalization is an essential goal in machine learning development since it directly affects the model's ability to perform in a live environment. Cross-validation is, therefore, an important step in validating the accuracy of a machine learning model before deploying it to a live setting. Many machine learning algorithms incorporate offline or local training of the model using labeled training data. Although a model can attain high accuracy with this training data, practitioners must determine whether you can reach the same accuracy with new data. Cross-validation is an effective technique for detecting over-fitting during the machine learning optimization process. Because over-fitted models are too tightly matched to training data, they will be erroneous with new data once deployed.

The following are the steps in cross-validation:

● Set aside a portion of the sample dataset.
● Train the model with the rest data set.
● Use the reserve sample of the data set to test the model.

Cross-Validation Methods


Under this technique, we perform training on half of the provided data while you use the remaining half for testing. The main disadvantage of this method is that we only train on half of the data set; it is feasible that the remaining data holds vital information that we are missing while trying to train our model, resulting in higher partiality.

Leave-One-Out Cross-Validation (LOOCV)

We train on the entire data set while leaving only one data point from the provided data and then iterate for each data point. This has some benefits and some drawbacks.

One benefit of this technique is that we use all data points, resulting in a low bias. Because we are testing against a single data point, this method has a higher variation in the testing model. If the data point is an outlier, the variation will be higher. Another disadvantage is that it takes longer to execute because it iterates over 'the number of data points' times.

K-Fold Cross-Validation

In K-fold cross-validation, we break down the data set into k subsets (folds), then train on all of them while leaving one (k-1) subset for evaluating the trained model. We iterate k times, each time with a specific subset best saved for testing purposes.

Benefits Of a Train/Test Split:

● Since K-fold cross-validation performs the test/train/test split K times, it runs K times quicker than Leave One Out cross-validation.
● Examining the detailed outcomes of the testing procedure is more effortless.

Advantages Of Cross-Validation:

● We eliminate out-of-sample accuracy more accurately.
● We use data more "efficiently" since we use each observation for both training and validation.

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