Minor changes

source/statistics/degree_of_freedom.rst

@@ -1,4 +1,4 @@
-Degree of freedom
+Degree of Freedom
 ===================
 
 BAM

source/statistics/index.rst

@@ -6,6 +6,6 @@ Statistics
    :maxdepth: 2
 
    metrics
-   dof
+   degree_of_freedom
 
 Statistics notes.

source/statistics/metrics.rst

@@ -50,6 +50,7 @@ Standard Error of the Mean (SEM) quantifies the error that is potentially made w
 Here is how to interpret it.
 If :math:`n=1`, the error is at most :math:`\sqrt{\mathbb{V}[X]}=\sigma_X` which is the standard deviation or :math:`X`.
 The more :math:`n` increases, the lower the error becomes.
+The greater :math:`\mathbb{V}[X]`, the greater :math:`n` needs to be to ensure a low :math:`\mathrm{SEM}`.
 More infos in `this video <https://www.youtube.com/watch?v=BwYj69LAQOI>`_.
 If it is still unclear, see the following R code: