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

**Jonathan Rougier
**
J.C.Rougier@durham.ac.uk

*Fri, 19 May 2000 09:57:10 +0100 (BST)*

On Fri, 19 May 2000, Prof Brian Ripley wrote:
>* > I was surprised to find that the variance of a scalar, using
*>* > var(), is NA. Surely this should be zero?
*>* >
*>*
*>* Do you mean a vector of length 1? (S has no scalars.) No, it should be
*>* NA, as sum((x-xbar)^2)/(n-1) is NaN, or, in statistical terms, one has
*>* no idea at all of the variability from a single sample.
*
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?
Jonathan Rougier Science Laboratories
Department of Mathematical Sciences South Road
University of Durham Durham DH1 3LE
http://www.maths.dur.ac.uk/stats/people/jcr/jcr.html
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