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Re: Puzzled by the "Variance"

  • To: mathgroup at smc.vnet.net
  • Subject: [mg86524] Re: Puzzled by the "Variance"
  • From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
  • Date: Thu, 13 Mar 2008 04:30:48 -0500 (EST)
  • Organization: Uni Leipzig
  • References: <fr8b97$h2s$1@smc.vnet.net>
  • Reply-to: kuska at informatik.uni-leipzig.de

Hi,

you are shure that varance is not

Sum[x[i]-Mean[x],{i,n}]/(n-1)

?

and your example should be

((1-2)^2+(2-2)^2+(3-2)^2)/2 -> 1

??

And any text book about statistics can tell you "Why?"
there is the factor 1/(n-1) and not 1/n.

Regards
   Jens


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??


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