[Rd] variance of a scalar (PR#546)

[Telford Tendys]

> > I thought that might be the reason.  There is no mention of using n-1
> > rather than n in the denominator on the help page.  Perhaps that might be
> > added?
> 
> Um. What professional statistics package uses n, then?  Are you
> suggesting that there is serious room for doubt?

I remember that my Casio calculator (in statistics mode) had some way
of setting the denominator to be n-1 or n so obviously someone at Casio
decided to cover both options. I was always taught to use n-1 but
I've been too lazy to work through the derivations and figure out why
one is better than the other.

I agree that a single sample cannot tell you anything about the variance
which is a good enough reason to convince me to keep using n-1.

	- Tel

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