Measures of Spread 2 - Standard Deviation

Another way of describing the spread of a distribution is by describing the differences between individual observations and the mean.
To do this we use the standard deviation(s).
The standard deviation is defined as the square root of the variance(s²).
The variance is found using the formula below:

It takes too long to work this out by hand, so use a calculator or a computer.

The standard deviation is heavily influenced by outliers, just like the mean, so it may not be meaningful in some situations.