Variance in R - dummies

# 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.