Minor changes

source/statistics/index.rst

@@ -5,6 +5,7 @@ Statistics
    :numbered:
    :maxdepth: 2
 
+   notations
    metrics
    bessel_correction
 

source/statistics/notations.rst

@@ -0,0 +1,30 @@
+Notations
+---------------
+
+This page was inspired from the following `Wikipedia page <https://en.wikipedia.org/wiki/Notation_in_probability_and_statistics>`_.
+
+
+Sample and Population
+=====================
+
+A *population* is the entire population that you want to analyze. It is a exhaustive set. A *sample* is a subset of the population. It is a non-exhaustive set.
+
+.. note::
+   TODO add figure
+
+*Statistics* allows you to infers properties on a population using samples with a certain degree of confidence.
+
+Notation: A Schizophrenia story
+================================
+Two different notation conventions are used. The one to use depends if you are working on a *population* or a *sample*:
+
+.. list-table:: Notation
+    :align: center
+            
+    * - Metric
+      - Population
+      - Sample
+    * - Sample mean
+      - :math:`\mu`
+      - :math:`\overline{x}`
+