Deviation Measures
The drawback of the range as a measure of dispersion is that it takes into account the values of only two data points - the largest and the smallest.
One way to have a dispersion measure that takes into account every data point is to use deviations. Deviation means difference. We can find the average of the deviations of the data points from a fixed value.
AP = deviation of A from P BP = deviation of B from P CP = deviation of C from P
AP = deviation of A from P
BP = deviation of B from P
CP = deviation of C from P
We can find average deviation of a set of observations from any fixed number.