A
parameter that indicates the way in which a probability function or a probability density
function is centred around its mean.
In other words how far away (on average) a result is from the mean.
To
calculate:
- Add together all items
- Divide the total by the number of items
- This is the mean
- Subtract each item from the mean
- Multiply each result by itself
- Add all these results together
- Divide by the total number of items
- This is the Variance
- The square root of the Variance is the standard deviation
The smaller it is (in
proportion to the
mean) the more likely the mean is to be a useful result and the less likely there are to be a few very high or very low results making the mean a bad
representation of the
data.