diff --git a/src/Phpml/Math/Statistic/Correlation.php b/src/Phpml/Math/Statistic/Correlation.php
index a6047a8..1d2e8ac 100644
--- a/src/Phpml/Math/Statistic/Correlation.php
+++ b/src/Phpml/Math/Statistic/Correlation.php
@@ -23,8 +23,8 @@ class Correlation
         }
 
         $count = count($x);
-        $meanX = array_sum($x) / $count;
-        $meanY = array_sum($y) / $count;
+        $meanX = Mean::arithmetic($x);
+        $meanY = Mean::arithmetic($y);
 
         $axb = 0;
         $a2 = 0;
diff --git a/src/Phpml/Math/Statistic/StandardDeviation.php b/src/Phpml/Math/Statistic/StandardDeviation.php
index a05faa4..2b03c54 100644
--- a/src/Phpml/Math/Statistic/StandardDeviation.php
+++ b/src/Phpml/Math/Statistic/StandardDeviation.php
@@ -28,7 +28,7 @@ class StandardDeviation
             throw InvalidArgumentException::arraySizeToSmall(2);
         }
 
-        $mean = array_sum($a) / $n;
+        $mean = Mean::arithmetic($a);
         $carry = 0.0;
         foreach ($a as $val) {
             $d = $val - $mean;