# [R] Standard Deviation in R

Greg Snow 538280 at gmail.com
Mon Jun 9 04:33:45 CEST 2014

```Which formula for standard deviation are you using?

If you know the population mean then you should divide by n (3 in this
case), but if you don't know the population mean and use the mean
calculated from the sample then it is more usual to use n-1 as the
denominator (this makes the variance an unbiased estimator of the
population variance).  That is what the R sd function does since it is
much more common to use it on a sample rather than an entire
population.

On Sun, Jun 8, 2014 at 1:17 AM, arun <smartpink111 at yahoo.com> wrote:
> Hi,
> http://stats.stackexchange.com/questions/25956/what-formula-is-used-for-standard-deviation-in-r
>
> A.K.
>
>
> It is my understanding that the R function SD finds the standard deviation of a random variable or a list. Please consider the following list: { 1, 2, 3 }. I claim that the standard deviation of this list is not 1. However, the following R statement returns 1:
>          sd ( seq(1:3) )
> What am I missing?
>
> I thank the group in advance for their responses.
>
> Bob
>
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help