diff --git a/source/index.rst b/source/index.rst
index 7f85282..d359a01 100644
--- a/source/index.rst
+++ b/source/index.rst
@@ -15,6 +15,8 @@ Welcome to ScienceNotes's documentation!
    statistics/metrics
    statistics/bessel_correction
    statistics/bayes_theorem
+   statistics/probability_distribution_functions.rst
+
 
 
 Indices and tables
diff --git a/source/statistics/probability_distribution_functions.rst b/source/statistics/probability_distribution_functions.rst
new file mode 100644
index 0000000..6915b74
--- /dev/null
+++ b/source/statistics/probability_distribution_functions.rst
@@ -0,0 +1,4 @@
+Probability Distribution Functions
+------------------------------------
+
+todo CDF and PDF