Data Science

Learn About Overfitting and Underfitting in Machine Learning

Published: 4th August, 2023

Harshini Bhat

Data Science Consultant at almaBetter

Understanding overfitting and underfitting in Machine Learning. Learn their impact, causes, and practical tips with examples for optimal model performance.

In the vast realm of Machine Learning, the ultimate goal is to build models that can generalize well to unseen data. Generalization refers to the ability of a model to accurately predict outcomes for new, unseen instances. However, two formidable challenges often arise in this pursuit: overfitting and underfitting. Overfitting and underfitting are two common pitfalls that can hinder the performance and reliability of Machine Learning models. To grasp these concepts, let's understand what is overfitting and underfitting in machine learning, their implications in Machine Learning and the difference between overfitting and underfitting in machine learning.

What is Underfitting in Machine Learning

Underfitting occurs when a model fails to capture the underlying patterns and relationships within the data. In other words, it is an oversimplified representation that struggles to generalize to new instances. Imagine an underconfident student who lacks a deep understanding of the subject matter. They might struggle to apply their knowledge to different problems.

Causes of Underfitting

Causes of underfitting can include using an overly simplistic model or insufficient training. This can lead to an excessively high bias, meaning the model has limited flexibility to learn complex patterns. As a result, the model may produce inaccurate predictions both on the training data and new, unseen data.

What is Overfitting in Machine Learning

On the opposite end of the spectrum, overfitting occurs when a model becomes too complex and starts to "memorize" the training data instead of learning the underlying patterns. This resembles an overconfident student who rote memorizes information without truly understanding the concepts.

When a model overfits, it performs exceptionally well on the training data, but fails to generalize to new data. The model has learned the noise and peculiarities of the training set, leading to poor performance on unseen instances. Overfitting often arises when the model has an excessively high variance, resulting in a lack of generalization ability.

Causes and Impacts of Overfitting

Overfitting, can stem from employing overly complex models with a large number of features or insufficient regularization. The consequences of overfitting include high variance, causing the model to fit the noise in the training data rather than capturing the true underlying patterns.

Underfitting and Overfitting

Underfitting and Overfitting

Preventive Measures and Techniques

To combat underfitting and overfitting, various preventive measures and techniques can be employed:

  1. Data preprocessing and feature engineering: By carefully preparing the data and selecting relevant features, the model can capture important patterns and reduce underfitting.
  2. Regularization techniques: L1 and L2 regularization introduce penalties for complex models, preventing overfitting and promoting generalization.
  3. Cross-validation: Dividing the data into training and validation sets helps assess model performance and prevent overfitting by optimizing hyperparameters.
  4. Early stopping: Monitoring the model's performance during training and stopping it at an optimal point helps prevent overfitting and find the right balance.

Model Evaluation and Diagnosis

To ensure the effectiveness of Machine Learning models, it is crucial to evaluate their performance accurately. By employing various evaluation metrics, we can gain insights into how well the model performs in different aspects. Metrics such as accuracy, precision, recall, and F1-score provide a comprehensive understanding of the model's ability to classify instances correctly, handle imbalances in the data, and strike a balance between precision and recall.

One powerful tool for assessing model performance is the confusion matrix. This matrix visually presents the model's predictions and reveals its strengths and weaknesses. It consists of four key components: true positives, true negatives, false positives, and false negatives. By analyzing the numbers in each cell, we can gain valuable insights into where the model excels and where it struggles, helping us identify areas for improvement.

Another useful technique for evaluating model performance is the use of learning curves. These curves allow us to analyze how the model performs over time as the training data size increases or the complexity of the model changes. By observing the learning curves, we can detect signs of overfitting or underfitting. Ideally, we would like to see steady increases in performance on both the training and validation sets, indicating that the model is learning effectively.

However, if the curves plateau or diverge, it may suggest overfitting, where the model is excessively fitting the training data. Conversely, if the performance is consistently low on both sets, it may indicate underfitting, where the model is unable to capture the underlying patterns.

To effectively tackle overfitting and underfitting, consider the following practical tips:

  1. Optimal Model Complexity:

    • Adjust hyperparameters (e.g., learning rate, number of layers) to find the right model complexity.
    • Regularly evaluate model performance on validation data to determine the optimal complexity.
  2. Gather Sufficient Data:

    • More data provides a broader representation of underlying patterns.
    • Reduces the risk of overgeneralization or oversimplification, alleviating both underfitting and overfitting.
  3. Adopt an Iterative Improvement Approach:

    • Learn from mistakes and adapt the model based on insights gained from evaluation.
    • Iteratively refine the model to enhance its performance over time.
  4. Emphasize Balance and Tradeoffs:

    • Understand the tradeoffs involved in model development.
    • Find the right balance between model complexity, training data size, and regularization techniques.
    • Striking this balance is crucial for mitigating underfitting and overfitting in machine learning, leading to improved generalization and model performance.


Understanding overfitting and underfitting is crucial for building reliable machine learning models. Overfitting occurs when models become too complex and memorize noise, while underfitting arises when models oversimplify the underlying patterns. By finding the balance between the two, we can develop models that generalize well and make accurate predictions on unseen data. By implementing techniques like data preprocessing, regularization, cross-validation, and early stopping, we can mitigate the risks of overfitting and underfitting. Remember, the goal is not to eliminate these phenomena entirely, but to strike the right balance that maximizes a model's generalization.

If you're interested in learning more about such concepts and pursuing a career as a Data Scientist.Click here to kickstart your career as a data scientist.

Related Articles

Top Tutorials

Made with heartin Bengaluru, India
  • Official Address
  • 4th floor, 133/2, Janardhan Towers, Residency Road, Bengaluru, Karnataka, 560025
  • Communication Address
  • 4th floor, 315 Work Avenue, Siddhivinayak Tower, 152, 1st Cross Rd., 1st Block, Koramangala, Bengaluru, Karnataka, 560034
  • Follow Us
  • facebookinstagramlinkedintwitteryoutubetelegram

© 2024 AlmaBetter