5. Standard Deviation


The standard deviation is nothing else than the square root of the variance. Unlike the variance, the standard deviation has the same unit as the mean, the median or any entry in the dataset. This makes it very useful as it can be used in combination with the mean to define how values are spread around the mean. Often, you will find this expressed as MEAN +/- SD .

In R, the standard deviation is obtained via the function sd(). Note that you will obtain the same result by calculating “manually” the square root of the variance sqrt(var()):

my.dataset <- c(1,2,3,4,5,6,7,8,9,10)
sd(my.dataset)
sqrt(var(my.dataset))

Skjermbilde 2016-05-20 22.39.11