Overfitting and Underfitting: Balancing Model Complexity

Pratik Kumar Roy
2 min readAug 10, 2023

In the realm of machine learning, two critical concepts stand out as challenges that need to be managed to create models that generalize well to unseen data: overfitting and underfitting. These terms describe the delicate balance between a model’s complexity and its ability to capture the underlying patterns in the data.

Overfitting: When the Model Learns Too Much

Definition: Overfitting occurs when a model learns the training data too well, including its noise and outliers. As a result, the model fits the training data almost perfectly, but its performance on new, unseen data drops significantly.

Causes:

Too Much Complexity: An overly complex model can fit even the tiniest fluctuations in the training data, leading to memorization rather than learning meaningful patterns.
Not Enough Data: When the training dataset is small, a complex model might capture random noise as if it were a pattern.
Too Many Features: If a model is fed with too many irrelevant features, it can inadvertently pick up on irrelevant noise.

Signs:

Low Training Error: The model’s error on the training data is extremely low, often approaching zero.
High Test Error: The model’s error on unseen test/validation data is much higher than on the training data.
Overly Complex Patterns: The model captures detailed noise in the data rather than general trends.

Remedies:

Regularization: Introducing penalties for large parameter values helps control model complexity.
Feature Selection: Choose relevant features and eliminate noise to provide the model with meaningful information.
More Data: Increasing the size of the training dataset can help the model learn genuine patterns instead of noise.

Underfitting: When the Model Learns Too Little

Definition:

Underfitting occurs when a model is too simple to capture the underlying patterns in the data. It fails to learn the complexities of the problem and performs poorly on both the training and unseen data.

Causes:

-Too Simple Model: If the model lacks the complexity to capture even the most basic relationships in the data, it will struggle to make accurate predictions.
Insufficient Training: Inadequate exposure to diverse and representative data can result in a model that doesn’t understand the problem.

Signs:

High Training Error: The model’s error on the training data is higher than expected.
High Test Error: The model’s error on new data remains high.
Undergeneralization: The model struggles to capture key trends and relationships in the data.

Remedies:

Complexify the Model: Introduce more complexity to the model by increasing the number of parameters or adding higher-order terms.
Feature Engineering: Add more relevant features that describe the problem better.
Try Different Algorithms: Sometimes, another algorithm might be better suited to the problem at hand.

Balancing Act: Finding the Sweet Spot

The key lies in finding the right balance between model complexity and generalization. The goal is to build models that can discern meaningful patterns while ignoring noise. Techniques like hyperparameter tuning, cross-validation, and utilizing various model evaluation metrics play pivotal roles in achieving this equilibrium, helping data scientists craft models that not only excel on training data but also generalize well to real-world scenarios.

Thanks for reading

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