Definition of Bagging

Bagging, short for “Bootstrap Aggregating,” is a machine learning ensemble technique that aims to improve the accuracy and stability of classification and regression models. It involves training multiple instances of the same base model on different subsets of the training dataset, derived by random sampling with replacement. The predictions from these models are then combined by voting for classification problems or averaging for regression problems to yield the final prediction.


The phonetics of the keyword “Bagging” is: /ˈbæɡɪŋ/

Key Takeaways

  1. Bagging, short for Bootstrap Aggregating, is an ensemble method used in machine learning to improve the accuracy and stability of a model by averaging the prediction results of multiple base learners.
  2. It reduces overfitting and variance in a model by training multiple base learners on different subsets of the data, generated by random sampling with replacement, and then combining their predictions using voting or averaging.
  3. Bagging works best when the base learners have high variance and low bias, such as decision trees, and is particularly effective for tasks like regression, classification and prediction.

Importance of Bagging

Bagging, or Bootstrap Aggregating, is an important technology term as it is a powerful ensemble learning technique used to improve the accuracy and stability of machine learning models.

By creating multiple sub-models using different subsets of the training data, bagging effectively reduces overfitting and minimizes errors due to high variance.

This approach provides a more robust and reliable final prediction by averaging or combining the outcomes of the individual models, thereby increasing generalization and enhancing overall performance.

In scenarios where complex data structures, noise, or outliers might hamper a single model’s accuracy, bagging proves to be a crucial method in delivering more accurate and consistent results.


Bagging, short for “bootstrap aggregating”, is an ensemble learning method widely used in the field of machine learning and data science to improve the performance and accuracy of predictive models. Its primary purpose is to reduce the variance and overfitting often observed in individual models, especially the ones built using decision trees and other high-variance algorithms. Bagging works by essentially creating a diverse selection of base models by training them on randomly drawn subsets of the original dataset, which are generated using a technique called bootstrapping.

This technique involves randomly sampling the data with replacement, producing multiple training sets that vary in terms of their data points. The bagging process not only addresses the common issues related to model overfitting and variance but also enhances the model’s ability to generalize well on unseen data. By training multiple models independently and then merging their predictions via a majority vote or averaging system, the overall prediction accuracy is increased.

Additionally, this process enhances model stability by cancelling out the influence of individual errors or biases, leading to a more robust aggregated model. Bagging is widely used in various real-world applications, including image recognition, speech processing, natural language processing, fraud detection, and recommender systems. Overall, bagging serves as a powerful tool to increase model accuracy and reliability when dealing with complex, high-variability datasets.

Examples of Bagging

Bagging, or Bootstrap Aggregating, is a machine learning technique used to improve the stability and accuracy of classification algorithms, regression models, and decision trees by creating multiple models and aggregating their results. Here are three real-world examples where bagging is used:

Healthcare: Bagging is employed in the development of diagnostic tools to identify diseases and abnormal conditions. For example, bagging has been used to create more reliable models for predicting the likelihood of diabetic retinopathy, a complication from diabetes that can cause blindness. By combining the outputs of multiple classifiers, the overall model is more robust and accurate, supporting doctors in making more well-informed decisions about patient diagnosis and treatment.

Finance: In finance, bagging is used to create models for predicting future stock prices or financial indicators. Financial institutions rely on these models for investment decision-making and risk management purposes. Bagging can improve the accuracy of predictions by combining the outputs of multiple weak learners, leading to more comprehensive and reliable forecasts for various financial instruments and markets.

Fraud Detection: One of the challenges in fraud detection is that fraudulent behaviors are often rare events and constantly evolving. Bagging can help improve detection rates by creating multiple models trained on different subsets of the data. These models can together form a more accurate and reliable predictor by aggregating individual predictions, identifying fraudulent transactions while minimizing false alarms. This technique is utilized in sectors like banking, insurance, and e-commerce to protect businesses and customers from fraudulent activities.

FAQ: Bagging

1. What is bagging?

Bagging, which stands for Bootstrap Aggregating, is an ensemble learning method that aims to reduce variance in a prediction model by combining multiple base models. It works by repeatedly bootstrapping random samples from the dataset and training separate models on each subsample, and then combining the outputs to create a more stable and accurate prediction.

2. When should we use bagging?

Bagging is particularly useful when dealing with high variance models that tend to overfit the training data. By averaging the outputs of multiple models, bagging can significantly reduce variance and improve prediction accuracy, making it ideal for use with unstable models such as decision trees or neural networks.

3. How does bagging compare to boosting and stacking?

Bagging, boosting, and stacking are all ensemble methods aimed at improving the performance of single prediction models. However, they work differently. While bagging reduces variance by averaging the outputs of multiple base models, boosting focuses on minimizing both bias and variance by iteratively improving the base models’ performance on misclassified instances, and stacking combines the outputs of multiple models through a meta-model, creating a potentially more accurate overall prediction strategy.

4. What are some popular bagging algorithms?

Some popular bagging algorithms include Bagging Classifier, Random Forest, and Extra Trees Classifier. Each of these methods combines multiple base models, usually decision trees, to create an aggregated prediction that aims to improve the stability and accuracy of a single model.

5. What are the limitations of bagging?

Some limitations of bagging include increased computation time due to the need to train multiple base models, the potential for overfitting when dealing with noisy or small datasets, and the fact that bagging can only improve the performance of unstable algorithms but may not provide a significant improvement over stable algorithms.

Related Technology Terms

  • Bootstrap Aggregating
  • Ensemble Learning
  • Decision Trees
  • Random Forests
  • Out-of-Bag Error

Sources for More Information


About The Authors

The DevX Technology Glossary is reviewed by technology experts and writers from our community. Terms and definitions continue to go under updates to stay relevant and up-to-date. These experts help us maintain the almost 10,000+ technology terms on DevX. Our reviewers have a strong technical background in software development, engineering, and startup businesses. They are experts with real-world experience working in the tech industry and academia.

See our full expert review panel.

These experts include:


About Our Editorial Process

At DevX, we’re dedicated to tech entrepreneurship. Our team closely follows industry shifts, new products, AI breakthroughs, technology trends, and funding announcements. Articles undergo thorough editing to ensure accuracy and clarity, reflecting DevX’s style and supporting entrepreneurs in the tech sphere.

See our full editorial policy.

More Technology Terms

Technology Glossary

Table of Contents