From 1e8c12067bb3dff40458b20c9dffe819b3bec1e2 Mon Sep 17 00:00:00 2001
From: Jason Davies <jason@jasondavies.com>
Date: Wed, 11 May 2011 16:52:37 +0100
Subject: [PATCH] Clarify d3.stats.variance.

Remove TODO comment as this seems numerically robust enough.  The same two-pass
algorithm is used in Haskell's "statistics" package.
---
 d3.stats.js           | 4 ++--
 src/stats/variance.js | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/d3.stats.js b/d3.stats.js
index 3ed8e942..a96a6986 100644
--- a/d3.stats.js
+++ b/d3.stats.js
@@ -142,8 +142,8 @@ d3.stats.quantiles = function(d, quantiles) {
     return ~~q === q ? (d[q] + d[q + 1]) / 2 : d[Math.round(q)];
   });
 };
-// TODO: replace with more stable algorithm.
-// Sample variance.
+// Unbiased estimate of a sample's variance.
+// Also known as the sample variance, where the denominator is n - 1.
 d3.stats.variance = function(x) {
   var mean = d3.stats.mean(x),
       n = x.length,
diff --git a/src/stats/variance.js b/src/stats/variance.js
index 21ebbd2b..fbd08f04 100644
--- a/src/stats/variance.js
+++ b/src/stats/variance.js
@@ -1,5 +1,5 @@
-// TODO: replace with more stable algorithm.
-// Sample variance.
+// Unbiased estimate of a sample's variance.
+// Also known as the sample variance, where the denominator is n - 1.
 d3.stats.variance = function(x) {
   var mean = d3.stats.mean(x),
       n = x.length,