what is cross validation in machine learning?

what is cross validation in machine learning?

As machine learning algorithms continue to gain popularity, it becomes increasingly essential to evaluate their performance accurately. In machine learning, cross-validation stands out as a popular technique employed to actively evaluate the performance of a predictive model. Understanding cross-validation enables practitioners to make informed decisions and improve the effectiveness of machine learning algorithms. In this article, we will dive deeper into what cross-validation is, its types, and how it works.

Introduction to Cross-Validation

Cross-validation is a valuable technique for assessing a model’s ability to generalize to new data. The fundamental concept behind cross-validation involves dividing the data into multiple subsets. By training the model on the training set and evaluating its performance on the validation set, we can iteratively repeat this process with different validation sets. This iterative approach allows us to obtain a comprehensive evaluation of the model’s performance. Cross-validation can help to reduce overfitting in the model. Overfitting occurs when a model excessively tailors its learning to the training data, hindering its ability to effectively generalize to new data. Cross-validation helps to prevent this by evaluating the model on several different subsets of the data.

Types of Cross-Validation

Depending on the dataset and the model at hand, various types of cross-validation techniques can be employed.Here are the most common types:

1. K-Fold Cross-Validation

K-Fold cross-validation is a highly popular and reliable technique used for evaluating models in various domains. This technique actively partitions the data into K subsets, with K-1 subsets used for training and the remaining subset for validation. By repeating this process K times, each subset serves as the validation data precisely once. Finally, the overall performance of the model is determined by averaging the results obtained from the K evaluations. The utilization of K-Fold cross-validation ensures a comprehensive and accurate assessment of model performance.

2. Leave-One-Out Cross-Validation

Leave-One-Out cross-validation iteratively trains the model on all data points except one, which is used for validation. Each data point in the dataset is systematically held out as a validation sample in Leave-One-Out cross-validation. This technique provides a comprehensive evaluation of the model’s performance by testing it against each data point individually. The computational complexity of Leave-One-Out cross-validation can be a challenge, especially when dealing with large datasets.

3. Stratified Cross-Validation

Stratified Cross-Validation is a useful approach to handle imbalanced datasets by maintaining the same proportion of the target variable in each fold as in the whole dataset. This technique effectively addresses the challenge of imbalanced class distribution and provides reliable model evaluation. By stratifying the data, the model can learn from representative samples of each class, leading to better performance. Stratified Cross-Validation helps mitigate biases and ensures that the evaluation process is fair and unbiased. It is commonly used in machine learning tasks where class imbalance is a concern, such as fraud detection or medical diagnosis.

4. Time-Series Cross-Validation

Time-Series Cross-Validation proves valuable in handling time-series data by splitting it into training and validation sets based on time. This technique acknowledges the temporal nature of the data and ensures evaluation of the model on unseen future data. By considering the time order, it captures time-dependent patterns and prevents data leakage. Time-Series Cross-Validation finds particular usefulness in forecasting and predicting future values as it simulates real-world scenarios more accurately. This technique helps assess the model’s ability to capture trends, seasonality, and other temporal dynamics present in the data.

How Cross-Validation Works

Here is a step-by-step process of how cross-validation works:

  1. Split the dataset into training and testing sets.
  2. Divide the training set into K subsets.
  3. Train the model on K-1 subsets and validate on the remaining subset.
  4. Iterate step 3 K times, actively employing each subset once for validation.
  5. Average the performance of the model over K validations to obtain the final performance.


Cross-validation actively evaluates models in machine learning, preventing overfitting and promoting generalization to new data. Researchers and practitioners employ different cross-validation techniques, including K-Fold, Leave-One-Out, Stratified, and Time-Series Cross-Validation, based on the dataset and model requirements. These techniques play a vital role in ensuring the reliability and effectiveness of model performance evaluation.


1. What is overfitting in machine learning?

Overfitting occurs when a model excessively learns to fit the training data, leading to its failure in generalizing to new data.

2. What is the purpose of cross-validation in machine learning?

To assess the generalization capability of a model and mitigate the risk of overfitting, cross-validation serves as a valuable tool.

3. How many times should K-Fold cross-validation be repeated?

K-Fold cross-validation should be repeated K times, where K is typically set to 5 or 10.

4. What is the difference between K-Fold and Leave-One-Out cross-validation?

K-Fold cross-validation entails splitting the data into K subsets, while on the other hand, Leave-One-Out cross-validation trains the model on all the data except for a single data point.

5. The Versatility of Cross-Validation: Application with Any Machine Learning Model

Absolutely! You have the flexibility to apply cross-validation to any machine learning model, whether it falls under regression, classification, or even clustering. This versatile technique serves as a valuable tool, enabling you to assess your model’s performance and generalization across different domains and algorithms. Through the application of cross-validation, you actively acquire valuable insights regarding the performance of your model on unseen data. Consequently, this ultimately enables the optimization of its overall effectiveness.


Recent Post

Request for a Call

Collaborate with the best in the industry. Let’s talk and get your project moving.


Thank You for Subscribing

Come Join Us.
Generative AI Workshop Hackathon!
Food And Drinks Provided


Chatbot Dialogflow CX Instructions

Contact Us For Questions