# About dev set and test set

**URL:** <https://community.deeplearning.ai/t/about-dev-set-and-test-set/131592>\
**Category:** Structuring Machine Learning Projects\
**Tags:** coursera-platform\
**Created:** [May 26, 2022, 8:15am UTC](https://community.deeplearning.ai/t/about-dev-set-and-test-set/131592 "2022-05-26T08:15:58Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![1004271927](https://avatars.discourse-cdn.com/v4/letter/1/eb9ed0/32.png) [@1004271927](https://community.deeplearning.ai/u/1004271927)\
**Post date:** [May 26, 2022, 8:15am UTC](https://community.deeplearning.ai/t/about-dev-set-and-test-set/131592/1 "2022-05-26T08:15:58Z")

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Should I use the dev set to iteratively train the model or just use it to detect the error rate？The answer might be wrong，but I want to know why.Thank you

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**Author:** ![alvaroramajo](https://sea1.discourse-cdn.com/dlai/user_avatar/community.deeplearning.ai/alvaroramajo/32/17572_2.png) [@alvaroramajo](https://community.deeplearning.ai/u/alvaroramajo)\
**Post date:** [May 26, 2022, 8:59am UTC](https://community.deeplearning.ai/t/about-dev-set-and-test-set/131592/2 "2022-05-26T08:59:35Z")

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Hi, @1004271927!

Dev set is normally used to check how well your trained model performs with unseen data. Guided with these results, you can adjust your hyperparameters to get better results. Nevertheless, as you tweak this values to maximize the metrics on dev set, you might end up overfitting this hyperparameters on the dev set. That’s the reason behind having an additional test set.

You may find this [post](https://community.deeplearning.ai/t/overfit-overtune-the-dev-set/129316) useful as well.