Variance and standard deviation

Variance is a measure of the average distance of the observations from their mean. You can think of it as representing how ‘spread out’ the data are. Very widely dispersed means higher variance. Example: you always drink one cup of copy a day. The variance of your drinking is zero. All the observations are on the mean (which is 1). BUT if you sometimes drink three cups (like me) for breakfast, sometimes none at all, then the variance won’t be zero.

The standard deviation is just the square root of the variance. We use the standard deviation because the variance is in ‘squared units’.

You don’t need to work out the variance or the standard deviation by hand using the equation BUT you do need to know:

what the variance and standard deviation are

their relationship to each other

how to get them in Excel