Standard deviation

Standard deviation is a way of indicating the average amount that the figures you have cluster around a mean value. It is used when you want to know how uncertain our values are. In other words, if we look at one value, how sure can we be that it gives us an good indication of reality.

If the standard deviation is low, our values are closer to the mean value. In a data set with a low standard deviation, any one value is likely to more closely represent a trend than in a data set with a high standard deviation. However, it doesn't necessarily mean that the value we have chosen does this. It only indicates that it is likely to.