What is Overfitting?

Imagine you’re studying for a test by memorizing every single question and answer. Sure, you’d ace that specific test, but what if the teacher throws in a new question? You’d be stuck.

That’s similar to overfitting in machine learning. The model gets so focused on memorizing the training data that it can’t handle new situations. It learns the quirks and noises in the data instead of the underlying patterns. This makes it bad at making predictions on unseen data, which is the whole point of machine learning!

To avoid overfitting, we keep some data aside to test the model on. If the model does great on the training data but poorly on the unseen test data, it’s a sign of overfitting. We then need to adjust the model to make it learn the general patterns, not just memorize every detail

What does overfitting entail?

In machine learning, when an algorithm fits training data too closely, or even exactly, it is said to be overfitting. This leaves the model unable to draw valid inferences or predictions from any data type other than the training set. 

Overfitting defeats the machine learning model’s aim. The ability to apply a model to new data is ultimately what enables us to employ machine learning algorithms daily for data classification and prediction.

A sample dataset is used in the construction of machine learning algorithms to train the model. However, if the model is very sophisticated or trains on sample data for an extended period, it may begin to learn the “noise,” or unimportant information, present in the dataset. When the noise is retained by the model and fits too closely to the training set, the model becomes “overfitted,” and it cannot generalize well to new data. If a model cannot generalize well to new data, then it will not be able to perform the classification or prediction tasks that it was intended for.

How can you ignore overfitting?

Imagine studying for a test by memorizing everything. You might do well on that specific test, but only on something new. Similarly, a model can memorize the training data too much and fail on unseen data. Early stopping helps prevent this by pausing the training before it memorizes the “noise” in the data.

  1. More Training Data: The more data you have, the better your model can learn general patterns instead of memorizing every detail. Think of it as having more practice problems to solve so you understand the concepts better.
  2. Pick the Important Stuff: Sometimes, you might have extra information (features) that’s unimportant. Feature selection helps identify the most relevant features, like focusing on the key concepts for the test instead of memorizing everything.
  3. Regularization: Regularization is like adding a penalty for memorizing too much detail. It discourages the model from focusing on noise and encourages it to learn the general patterns.
  4. Strength in Numbers: Ensemble methods combine multiple models, like having a study group discuss different approaches to a problem. By combining their predictions, you get a more robust and accurate result.


What exactly is overfitting in machine learning? 

Overfitting occurs in machine learning when a model learns the details and noise in the training data to the extent that it negatively impacts the model’s performance on unseen data. Essentially, the model fits too closely to the training set, capturing even the irrelevant or random fluctuations, which makes it less effective in making predictions or classifications on new data. This phenomenon reduces the model’s ability to generalize from the training data to real-world scenarios.

How can overfitting be detected in a machine learning model? 

Overfitting is typically detected by evaluating the model’s performance on both the training data and a separate test dataset that it hasn’t seen during training. If the model shows high accuracy on the training data but performs poorly on the test data, it is likely overfitting. Other signs include a significant difference between training and test performance metrics, such as accuracy, precision, recall, or loss functions.

What are some practical methods to prevent overfitting in machine learning? Preventing overfitting involves several strategies:

  • Early Stopping: Halting the training process before the model starts to overfit the training data excessively.
  • More Training Data: Increasing the size of the training dataset helps the model generalize better by learning broader patterns instead of memorizing specific details.
  • Feature Selection: Identifying and using only the most relevant features (variables) that contribute to the predictive power of the model, ignoring irrelevant or noisy features.
  • Regularization: Introducing penalties in the model training process to discourage complex models that fit the training data too closely. Techniques like L1 (Lasso) and L2 (Ridge) regularization are commonly used for this purpose.

Why is overfitting detrimental to machine learning models? 

Overfitting undermines the fundamental purpose of machine learning, which is to create models capable of making accurate predictions on unseen data. When a model overfits, it loses its ability to generalize beyond the training set, leading to poor performance in real-world applications. This limits the model’s utility in tasks like classification, regression, and prediction, where reliability and robustness are essential.