> For the complete documentation index, see [llms.txt](https://fall2019.fullstackdeeplearning.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://fall2019.fullstackdeeplearning.com/course-content/training-and-debugging/evaluate.md).

# Evaluate

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Evaluate - Troubleshooting
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## Summary

* You want to apply **the bias-variance decomposition** concept here: *Test error = irreducible error + bias + variance + validation overfitting*.
* If the training, validation, and test sets come from different data distributions, then you should use **2 validation sets**: one set sampled from the training distribution, and the other set sampled from the test distribution.