# Variance in R

Calculating variance in R is simplicity itself. You use the `var() `

function. But which variance does it give you? The one with *N* in the denominator or the one with *N-*1? Time to find out:

`heights <- c(50, 47, 52, 46, 45)`

`> var(heights)`

`[1] 8.5`

It calculates the estimated variance (with *N*–1 in the denominator). To calculate that first variance with *N* in the denominator, you have to multiply this number by (*N*–1)/*N*. Using `length() `

to calculate *N*, that’s

`var(heights)*(length(heights)-1)/length(heights)`

`[1] 6.8`

If you were going to work with this kind of variance frequently, define a function `var.p()`

:

`var.p = function(x){var(x)*(length(x)-1)/length(x)}`

And here’s how to use it:

`> var.p(heights)`

`[1] 6.8`

Think of the denominator of a variance estimate (like N–1) as degrees of freedom.