diff --git a/source/statistics/index.rst b/source/statistics/index.rst
index 08bcb9f..75988cb 100644
--- a/source/statistics/index.rst
+++ b/source/statistics/index.rst
@@ -3,8 +3,8 @@ Statistics
 
 .. toctree::
    :maxdepth: 2
+   :numbered:
 
-   self
    introduction
 
 dlkdd
diff --git a/source/statistics/introduction.rst b/source/statistics/introduction.rst
index 9fba27b..f1f7691 100644
--- a/source/statistics/introduction.rst
+++ b/source/statistics/introduction.rst
@@ -72,3 +72,7 @@ Output example:
    ----- Experiment 3 -----
    Means SD: 1.27
    SEM       1.26
+
+
+Degree of freedom
+-------------------