diff --git a/fave/extractFormants.py b/fave/extractFormants.py
index 21c404b..8e2f76a 100755
--- a/fave/extractFormants.py
+++ b/fave/extractFormants.py
@@ -1068,20 +1068,14 @@ def maximumIntensity(intensities, times):
 def mean_stdv(valuelist):
     """returns the arithmetic mean and sample standard deviation (N-1 in the denominator) of a list of values"""
 
-    n = len(valuelist)
-    if n > 0:
-        if n == 1:
+    np_valuelist = np.array(valuelist,dtype=np.float64)
+    if len(np_valuelist) > 0:
+        if len(np_valuelist) == 1:
             mean = valuelist[0]
             stdv = 0
         else:
-            sum_i = 0
-            for i in range(n):
-                sum_i += valuelist[i]
-            mean = sum_i / n
-            diffsum_i = 0
-            for i in range(n):
-                diffsum_i += (valuelist[i] - mean) ** 2
-            stdv = math.sqrt(diffsum_i / (n - 1))
+            mean = np.nanmean(np_valuelist)
+            stdv = np.nanstd(np_valuelist, ddof=1)
 
     else:  # empty list
         mean = None
diff --git a/tests/fave/extract/test_extractFormants.py b/tests/fave/extract/test_extractFormants.py
index e30ebe6..362dbd1 100644
--- a/tests/fave/extract/test_extractFormants.py
+++ b/tests/fave/extract/test_extractFormants.py
@@ -1,4 +1,5 @@
 
+from cmath import nan
 import logging
 import pytest
 import numpy as np
@@ -42,7 +43,7 @@ def provide_valuelist():
             [-1],
             np.mean([-1]),
             0
-        ]
+        ],
         [
             [3.5, 2.6, 11.6, None, 34.66, 2.8, 4.7],
             np.nanmean(np.array([3.5, 2.6, 11.6, None, 34.66, 2.8, 4.7],