diff --git a/src/Stat.php b/src/Stat.php
index c4d816d..193f300 100644
--- a/src/Stat.php
+++ b/src/Stat.php
@@ -346,6 +346,8 @@ public static function harmonicMean(array $data, ?array $weights = null, ?int $r
      * Covariance is a measure of the joint variability of two inputs.
      * @param array<int|float> $x
      * @param array<int|float> $y
+     * @throws InvalidDataInputException if 2 arrays have different size,
+     * or if the length of arrays are < 2, or if the 2 input arrays has not numeric elements
      * @return false|float
      */
     public static function covariance(array $x, array $y): false|float
@@ -396,6 +398,9 @@ public static function covariance(array $x, array $y): false|float
      * and 0 no linear relationship.
      * @param array<int|float> $x
      * @param array<int|float> $y
+     * @throws InvalidDataInputException if 2 arrays have different size,
+     * or if the length of arrays are < 2, or if the 2 input arrays has not numeric elements,
+     * or if the elements of the array are constants
      * @return false|float
      */
     public static function correlation(array $x, array $y): false|float
diff --git a/tests/StatTest.php b/tests/StatTest.php
index 58ab431..44857a8 100644
--- a/tests/StatTest.php
+++ b/tests/StatTest.php
@@ -319,5 +319,5 @@
             [2, 2, 2]
         )
     )->toThrow(InvalidDataInputException::class);
-    
+
 });