Bagging vs Boosting in Machine Learning: Difference Between Bagging and Boosting
Updated on Jul 08, 2025 | 14 min read | 94.08K+ views
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Updated on Jul 08, 2025 | 14 min read | 94.08K+ views
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Did you know? In bagging, each bootstrap sample contains only about 63.2% of unique data points from the original dataset: the rest are duplicates! |
Bagging vs Boosting in Machine Learning boils down to how each improves model performance. Bagging reduces variance by combining independent models, such as Random Forest used in fraud detection. Boosting, on the other hand, reduces bias by correcting errors sequentially. XGBoost is a common choice for tasks like ad click prediction.
Both are ensemble methods, but they differ in how models are built and combined. In this blog, you'll explore their key differences, benefits, popular algorithms, and when to use each for practical machine learning tasks.
Bagging injects randomness through bootstrap sampling and then averages the results, giving reliable out-of-bag error estimates and taming overfitting-prone models. Boosting, instead, re-weights misclassified cases so each new learner tackles the toughest examples, gradually uncovering subtle, non-linear signals.
Bagging thrives on noisy data and unstable algorithms like full-depth trees, while Boosting excels when a slightly biased learner can be refined step-by-step. Together they show two complementary routes to stronger ensembles: one stabilises, the other sharpens.
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Understanding these techniques is crucial because they can drastically enhance the predictive power of your models, especially for tasks in data science and machine learning.
Here’s a side-by-side comparison of difference between bagging and boosting:
Feature | Bagging | Boosting |
Purpose | Reduces variance in high-variance models | Reduces bias by sequentially correcting model errors |
Model Independence | Models are trained independently, in parallel | Models are dependent, with each model correcting the last |
Weighting of Models | Equal weight given to all models | Weights are adjusted based on performance |
Training Data | Each model uses random subsets with replacement | Each model focuses on data points misclassified by the previous model |
Popular Example | Random Forest | AdaBoost, Gradient Boosting |
Best For | High-variance models like decision trees | High-bias models where sequential adjustments are helpful |
Iterative Process | Not iterative; models don’t depend on one another | Iterative; each model is trained based on previous results |
Combining Predictions | Aggregates predictions by voting or averaging | Combines weighted predictions based on accuracy |
Application Use Cases | Suitable for data with more noise and variability | Suitable for datasets where accuracy improvement is needed over multiple iterations |
Parallelism | Parallel processing of models | Sequential processing for error correction |
Now that you understand the core concepts of bagging vs boosting, it’s time to apply this knowledge. Start by experimenting with both techniques using real-world datasets. Begin with Bagging, as it’s easier to implement, especially with algorithms like Random Forest. To get a deeper understanding of how Bagging works and how it reduces variance, let’s dive into its inner workings.
Bagging, short for Bootstrap Aggregating, improves the performance of machine learning models by reducing variance through ensemble learning. To fully understand how Bagging works, it’s important to grasp a few key concepts that make this method effective.
1. Dataset Splitting (Bootstrap Sampling)
Bagging uses row sampling with replacement, meaning each subset drawn from the original dataset can have duplicate rows. This process creates multiple, unique subsets of data, each used to train an independent model.
In applications like financial forecasting, where variability and noise are common, this technique ensures that the model isn't overly influenced by specific outliers or trends that don’t generalize well.
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2. Independent Model Training
Each model is trained in parallel on its subset, ensuring each learns different aspects of the dataset. This parallel training makes Bagging computationally efficient when enough hardware resources are available. It speeds up the process, making it ideal for large datasets.
In image classification tasks, where large datasets are common, Bagging allows multiple models to train simultaneously, speeding up the process without compromising accuracy.
Also Read: Classification Model using Artificial Neural Networks (ANN)
3. Averaging Predictions
The predictions from each model are combined to form the final output. In classification tasks, this might be a majority vote; in regression, it could be the average of predictions. This aggregation reduces overfitting and variance, improving overall accuracy.
In medical diagnosis or spam detection, where predictions need to be highly accurate, Bagging ensures that random fluctuations in data don't drastically alter the final model's predictions.
Also Read: 12+ Machine Learning Applications Enhancing The Healthcare Sector In 2025
Start by applying Bagging techniques to different datasets, and observe how varying the number of models (estimators) or tuning other parameters affects your model's performance.
One of the best ways to solidify your understanding is by implementing Bagging in a real-life application.
Problem Statement: Predicting Customer Churn
Customer churn refers to when customers stop doing business with a company. For this example, we'll use a Customer Churn dataset to predict whether a customer will churn (leave) or stay based on various features like demographics, usage behavior, and services.
Step 1: Load and Preprocess the Data
First, let’s load the data and preprocess it. We'll encode categorical features (like gender or contract type) and split the dataset into training and testing sets.
import pandas as pd
from sklearn.model_selection import train_test_split
from sklearn.preprocessing import LabelEncoder
# Load dataset (replace with your file path)
data = pd.read_csv('customer_churn.csv')
# Encode categorical columns (e.g., gender, contract type)
label_encoder = LabelEncoder()
data['gender'] = label_encoder.fit_transform(data['gender'])
data['Churn'] = label_encoder.fit_transform(data['Churn']) # Target variable
# Define features (X) and target variable (y)
X = data.drop('Churn', axis=1)
y = data['Churn']
# Split the data into training and test sets (80% train, 20% test)
X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.2, random_state=42)
Step 2: Train a Bagging Model (Random Forest)
Now, we will train a Random Forest Classifier, which uses Bagging to predict customer churn. We’ll use 50 decision trees in the ensemble.
from sklearn.ensemble import RandomForestClassifier
from sklearn.metrics import classification_report
# Initialize the Random Forest model (uses Bagging under the hood)
model = RandomForestClassifier(n_estimators=50, random_state=42)
# Train the model on the training data
model.fit(X_train, y_train)
# Make predictions on the test set
y_pred = model.predict(X_test)
# Evaluate the model's performance
print(classification_report(y_test, y_pred))
Step 3: Evaluate the Model
The classification report will provide important metrics like precision, recall, F1-score, and accuracy. These are essential for understanding how well the model predicts customer churn and helps make business decisions.
Expected Output:
The output will show performance metrics like:
precision recall f1-score support
0 0.95 0.98 0.96 100
1 0.91 0.81 0.86 50
accuracy 0.94 150
macro avg 0.93 0.89 0.91 150
weighted avg 0.94 0.94 0.94 150
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Also Read: A Guide to the Top 15 Types of AI Algorithms and Their Applications
Start experimenting with different datasets and tweak the number of estimators or the base model to see how it impacts performance. Try applying Bagging to tasks with high variance, like image classification or financial forecasting, and observe how it reduces overfitting.
Once you feel confident with Bagging, the next step is to explore Boosting, another powerful ensemble technique that reduces bias by sequentially correcting model errors.
Boosting is a sequential ensemble technique combining multiple weak models to build a powerful model. In Boosting, each model tries to correct the errors made by its predecessor, leading to a highly accurate final model. This approach is especially effective for reducing bias in the model, making it popular for tasks requiring high precision.
Different types of boosting algorithms exist to improve model performance by focusing on correcting the errors of weak learners. Unlike Bagging, which reduces variance by training multiple models independently, Boosting works by sequentially training models, where each new model tries to correct the mistakes of the previous one.
This makes Boosting especially effective for reducing bias and improving accuracy.
1. AdaBoost (Adaptive Boosting)
2. Gradient Boosting
3. XGBoost (Extreme Gradient Boosting)
Now that you’ve explored the various types of Boosting algorithms, it's time to experiment with them on your own datasets. Start by applying AdaBoost for simpler tasks and gradually move on to more complex ones with Gradient Boosting or XGBoost.
Tune hyperparameters like learning rate and number of estimators to see their impact on performance.
Once you feel comfortable with the theory and the different algorithms, you can explore real-world applications, such as customer segmentation or predictive maintenance.
Real-Life Application: Fraud Detection in Financial Transactions
Fraud detection is critical in industries like banking and e-commerce, where identifying fraudulent transactions in real-time is essential for minimizing losses. Boosting algorithms like Gradient Boosting are highly effective here because they sequentially improve on weak models, learning from previous mistakes to handle complex, imbalanced datasets.
1. Load and Preprocess the Data
For this example, assume you have a Fraud Detection dataset where features represent transaction details (e.g., amount, time, merchant) and the target is whether the transaction is fraudulent (1 for fraud, 0 for legitimate).
import pandas as pd
from sklearn.model_selection import train_test_split
from sklearn.ensemble import GradientBoostingClassifier
from sklearn.metrics import classification_report
from sklearn.preprocessing import LabelEncoder
# Load dataset (replace with actual dataset)
data = pd.read_csv('fraud_detection.csv')
# Preprocessing: Encode categorical variables (e.g., merchant type)
label_encoder = LabelEncoder()
data['merchant'] = label_encoder.fit_transform(data['merchant'])
data['is_fraud'] = label_encoder.fit_transform(data['is_fraud']) # Target variable
# Features and target variable
X = data.drop('is_fraud', axis=1)
y = data['is_fraud']
# Split the data into training and test sets (80% train, 20% test)
X_train, X_test, y_train, y_test = train_test_split(X, y, test_size=0.2, random_state=42)
2. Train Gradient Boosting Classifier
# Initialize GradientBoostingClassifier
gb_model = GradientBoostingClassifier(n_estimators=100, learning_rate=0.1, random_state=42)
# Train the model
gb_model.fit(X_train, y_train)
# Make predictions on the test set
y_pred = gb_model.predict(X_test)
3. Evaluate the Model
# Evaluate the model's performance using classification report
print(classification_report(y_test, y_pred))
Expected Output:
precision recall f1-score support
0 0.98 0.97 0.97 950
1 0.87 0.92 0.89 150
accuracy 0.96 1100
macro avg 0.92 0.94 0.93 1100
weighted avg 0.96 0.96 0.96 1100
Explanation:
After implementing Boosting for fraud detection, the next actionable steps include tuning hyperparameters such as the number of estimators (n_estimators) and learning rate to further optimize performance.
It's also important to compare with other models like Random Forest or Logistic Regression to assess how different algorithms perform on the same task.
Additionally, consider feature engineering by incorporating more transaction-related features, such as merchant location or transaction history, to enhance the model's predictive accuracy.
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Now that we've explored the unique characteristics of Bagging and Boosting, let’s examine the similarities between these two powerful ensemble methods.
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Despite their different strategies, both bagging and boosting methods rely on aggregating predictions to produce a final, stronger model. Both methods improve model accuracy by combining predictions from multiple base models.
This is especially useful in tasks like customer churn prediction, where small gains in accuracy can lead to significant business benefits. Recognizing these similarities will help you make informed choices for your projects.
Let’s explore these shared aspects and their impact on machine learning tasks.
Feature |
Bagging & Boosting |
Ensemble Learning |
Both are ensemble techniques designed to combine multiple models, leveraging the strengths of each for a stronger overall model. |
Base Model Usage |
They both use base learners, typically weak classifiers, and aggregate their results to produce a strong prediction. |
Reduction of Variance |
Both aim to reduce errors in the final model, with Bagging reducing variance and Boosting reducing bias. |
Combining Predictions |
The final prediction is made by averaging or taking the majority vote of the models’ predictions. |
Application |
Both are commonly used in supervised learning tasks like classification and regression. |
Model Improvement |
They enhance model performance by iterating over weak models to correct or reduce errors. |
Feature Importance |
Both methods can produce feature importance scores, helping identify the key drivers of the model. |
Parallelism |
Bagging builds models in parallel, while Boosting typically builds them sequentially. Both involve multiple models that work together. |
Final Prediction |
The final prediction combines the output of all models to achieve higher accuracy and robustness. |
Also Read: 50+ Essential Deep Learning Interview Questions and Answers for Success in 2025
With a clear understanding of Bagging vs Boosting, you can deepen your knowledge of Machine Learning with upGrad!
By now, you now have a solid understanding of the key difference between Bagging and Boosting in machine learning. Bagging helps reduce variance by training models independently, while Boosting minimizes bias through sequential learning. Mastering when to use each method is essential for building more accurate and efficient models.
If you're looking to apply these techniques to real-world projects but need more guidance, upGrad’s AI and ML courses can help. With hands-on projects and personalized mentorship, these courses will empower you to tackle challenges and fast-track your career growth in the dynamic field of machine learning.
In addition to the courses mentioned above, here are some free courses by upGrad that can further strengthen your foundation in AI and ML.
Feeling uncertain about where to go next in your machine learning path? Consider availing upGrad's personalized career counseling. They can guide you in choosing the best path tailored to your goals. You can also visit your nearest upGrad center and start hands-on training today!
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Reference:
https://medium.com/@pacosun/the-secret-sauce-behind-random-forests-c5d77d850d3c
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