```{include} /../core/dataserver/attribute/introducing_tstochastic_attribute/student_title.md
```

```{include} /../core/dataserver/attribute/introducing_tstochastic_attribute/student_equation.md
```

This distribution is famous for the t-test, a test-hypothesis developed by Fisher to check validity of 
the null hypothesis when the variance is unknown and the number of degree-of-freedom is limited. 
Indeed, when the number of degree-of-freedom grows, the shape of the curve looks more and more like 
the centered-reduced normal distribution. The mean value of the student law is 0 as soon as $k > 1$ 
(and is not determined otherwise). Its variance can be written as $\sigma^2=\frac{k}{k-2}$ as soon 
as $k > 2$, infinity if $1 < k \leq 2$, and is not determined otherwise.

```{include} /../core/dataserver/attribute/introducing_tstochastic_attribute/student_figure.md
```