From: Scott Gasch <scott@gasch.org>
Date: Fri, 11 Feb 2022 19:14:20 +0000 (-0800)
Subject: Fix stdev.
X-Git-Url: https://wannabe.guru.org/gitweb/?a=commitdiff_plain;h=699219341e92365b7aa2f84df0c141bc4f0aa238;p=python_utils.git

Fix stdev.
---

diff --git a/math_utils.py b/math_utils.py
index 31610ba..3a672da 100644
--- a/math_utils.py
+++ b/math_utils.py
@@ -25,7 +25,7 @@ class NumericPopulation(object):
     >>> pop.get_mean()
     5.2
     >>> round(pop.get_stdev(), 2)
-    6.99
+    1.75
     >>> pop.get_percentile(20)
     3
     >>> pop.get_percentile(60)
@@ -80,7 +80,8 @@ class NumericPopulation(object):
             variance += (n - mean) ** 2
         for n in self.highers:
             variance += (n - mean) ** 2
-        return math.sqrt(variance)
+        count = len(self.lowers) + len(self.highers) - 1
+        return math.sqrt(variance) / count
 
     def get_percentile(self, n: float) -> float:
         """Returns the number at approximately pn% (i.e. the nth percentile)