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Re: Puzzled by the "Variance"

  • To: mathgroup at smc.vnet.net
  • Subject: [mg86537] Re: [mg86506] Puzzled by the "Variance"
  • From: DrMajorBob <drmajorbob at bigfoot.com>
  • Date: Thu, 13 Mar 2008 04:33:15 -0500 (EST)
  • References: <31283773.1205350347270.JavaMail.root@m08>
  • Reply-to: drmajorbob at longhorns.com

Variance gives the "unbiased estimate" of true variance based on a sampl=
e:

test = {1, 2, 3}
Variance@test

{1, 2, 3}

1

biased[x_List] := #.# &[x - Mean@x]/Length@test
biased@test

2/3

or...

biased[x_List] := (Length@x - 1)/Length@x Variance@x
biased@test

2/3

Bobby

On Wed, 12 Mar 2008 05:29:07 -0500, Elements <philyer at gmail.com> 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.ht=
ml.
> 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??



-- =

DrMajorBob at longhorns.com


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