[R] population variance and sample variance

[Ista Zahn]

Probably a simple typo, but just to keep things straight: you want to
divide by n when describing the standard deviation of a sample, and
divide by n-1 when estimating a population standard deviation (your
initial description had it backwards I think).

On Tue, Feb 2, 2010 at 5:25 PM, Peng Yu <pengyu.ut at gmail.com> wrote:
> On Mon, Oct 19, 2009 at 12:53 PM, Kingsford Jones
> <kingsfordjones at gmail.com> wrote:
>>> sum((x-mean(x))^2)/(n)
>> [1] 0.4894708
>>> ((n-1)/n) * var(x)
>> [1] 0.4894708
>
> But this is not a built-in function in R to do so, right?
>
>> hth,
>> Kingsford
>>
>> On Mon, Oct 19, 2009 at 9:30 AM, Peng Yu <pengyu.ut at gmail.com> wrote:
>>> It seems that var() computes sample variance. It is straight forward
>>> to compute population variance from sample variance. However, I feel
>>> that it is still convenient to have a function that can compute
>>> population variance. Is there a population variance function available
>>> in R?
>>>
>>> $ Rscript var.R
>>>> set.seed(0)
>>>> n = 4
>>>> x = rnorm(n)
>>>> var(x)
>>> [1] 0.6526278
>>>> sum((x-mean(x))^2)/(n-1)
>>> [1] 0.6526278
>>>>
>>>
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>>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>>>
>>
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>



-- 
Ista Zahn
Graduate student
University of Rochester
Department of Clinical and Social Psychology
http://yourpsyche.org