# Specifying nu for StudentT

**URL:** <https://discourse.pymc.io/t/specifying-nu-for-studentt/2528>\
**Category:** Questions\
**Created:** [January 15, 2019, 2:25pm UTC](https://discourse.pymc.io/t/specifying-nu-for-studentt/2528 "2019-01-15T14:25:02Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![jordan.howell2](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.pymc.io/jordan.howell2/32/1742_2.png) [@jordan.howell2](https://discourse.pymc.io/u/jordan.howell2)\
**Post date:** [January 15, 2019, 2:25pm UTC](https://discourse.pymc.io/t/specifying-nu-for-studentt/2528/1 "2019-01-15T14:25:03Z")

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Hello. I’m running a regression model using and using a StudentT distribution for the first time. That said, am I right in assuming the value for nu should be the len(observed Y - 1)?

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**Author:** ![junpenglao](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.pymc.io/junpenglao/32/8_2.png) [@junpenglao](https://discourse.pymc.io/u/junpenglao)\
**Post date:** [January 15, 2019, 3:26pm UTC](https://discourse.pymc.io/t/specifying-nu-for-studentt/2528/2 "2019-01-15T15:26:30Z")

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There is no restriction, you can set it to any positive value or random variable. In practice it shapes the tail of the distribution, so it dependence on how heavy tail you want your distribution to be.

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**Author:** ![jordan.howell2](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.pymc.io/jordan.howell2/32/1742_2.png) [@jordan.howell2](https://discourse.pymc.io/u/jordan.howell2)\
**Post date:** [January 15, 2019, 3:34pm UTC](https://discourse.pymc.io/t/specifying-nu-for-studentt/2528/3 "2019-01-15T15:34:06Z")

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Thank you @junpenglao

Ok. Any best practices? I thought it represented the degrees of freedom. Is that right?

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**Author:** ![junpenglao](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.pymc.io/junpenglao/32/8_2.png) [@junpenglao](https://discourse.pymc.io/u/junpenglao)\
**Post date:** [January 15, 2019, 3:41pm UTC](https://discourse.pymc.io/t/specifying-nu-for-studentt/2528/4 "2019-01-15T15:41:49Z")

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It does, but the usage is different than when you are using it for t-test and getting p values.  
Best practice is to set it to a small value, after nu \> 30 you get something quite close to Gaussian

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<div class="post-metadata">

**Author:** ![jordan.howell2](https://yyz2.discourse-cdn.com/flex036/user_avatar/discourse.pymc.io/jordan.howell2/32/1742_2.png) [@jordan.howell2](https://discourse.pymc.io/u/jordan.howell2)\
**Post date:** [January 15, 2019, 3:42pm UTC](https://discourse.pymc.io/t/specifying-nu-for-studentt/2528/5 "2019-01-15T15:42:50Z")

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Alright then. Thank you!