Elena' s AI Blog

Cross-Validation Techniques

13 Mar 2025 (updated: 24 Aug 2026) / 27 minutes to read

Elena Daehnhardt

Midjourney 6.1: cross-validation color graphs


TL;DR:
  • Never trust a model evaluated only on its training data. Use cross-validation (like K-Fold or Stratified K-Fold for imbalanced data) to get a realistic estimate of how your model will perform in the real world.

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Cross-Validation in Machine Learning: Why It Matters

In machine learning, building a model that performs perfectly on your training data is relatively easy. The real challenge is ensuring that the model performs just as well on data it has never seen before. If you don’t evaluate this properly, you risk deploying an overfitted model that fails spectacularly in production.

Cross-validation is a model-validation technique that estimates how well a machine learning model generalises to unseen data by repeatedly splitting the dataset into training and validation subsets. It is the gold standard for assessing generalisation.

In this post, we will explore the concept of generalisation and implement various cross-validation techniques using the Titanic dataset and The Daily Minimum Temperatures dataset (for time series splits). All implementations will use scikit-learn.

Prerequisites: Python Libraries for Cross-Validation

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Understanding Generalisation in Machine Learning

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What Is Cross-Validation?

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The Main Purpose of Cross-Validation

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Cross-Validation and the Bias-Variance Tradeoff

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Learning Curves in scikit-learn

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Different Cross-Validation Techniques

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Using GPU in Colab with scikit-learn

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Further Reading on Cross-Validation

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Cross-Validation Best Practices

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Conclusion: Choosing the Right Cross-Validation Technique

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References

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About Elena

Elena, a PhD in Computer Science, simplifies AI concepts and helps you use machine learning.






Citation
Elena Daehnhardt. (2025) 'Cross-Validation Techniques', daehnhardt.com, 13 March 2025. Available at: https://daehnhardt.com/blog/2025/03/13/cross-validation/
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