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Re: Puzzled by the "Variance"

• To: mathgroup at smc.vnet.net
• Subject: [mg86520] Re: Puzzled by the "Variance"
• From: "Kevin J. McCann" <Kevin.McCann at umbc.edu>
• Date: Thu, 13 Mar 2008 04:30:04 -0500 (EST)
• Organization: University System of Maryland
• References: <fr8b97$h2s$1@smc.vnet.net>

The answer is, I believe, in the article you quote. The gist of it is 
that you divide by (n-1) not n for an unbiased estimator of the 
variance. To see that Mathematica is actually doing this, I commend to you the 
Help on Variance.

Kevin

Elements wrote:
> Greeting all
> I'm puzzled by the function "Variance". We can learn how to calculate
> variance from this page:http://mathworld.wolfram.com/SampleVariance.html.
> For example, calculate the sample variance of {1,2,3}. the average of
> {1,2,3} is 2, then the variance should be ((1-2)^2+(2-2)^2+(3-2)^2)/3=2/3.
> But mathematica gives that:
> 
> In[10]:= Variance[{1.0,2.0,3.0}]
> Out[10]= 1.
> 
> Why??

-- 

Kevin J. McCann
Research Associate Professor
JCET/Physics
Physics Building
University of Maryland, Baltimore County
1000 Hilltop Circle
Baltimore, MD 21250