Mean deviation is a statistical measure of the average deviation of values from the mean in a sample. It is calculated first by finding the average of the observations. The difference of each observation from the mean then is determined. The deviations then are averaged. This analysis is used to calculate how sporadic observations are from the mean.

List data values in a column, for example:

2 5 7 10 12 14

Find the average of these values by adding them and then and dividing them by the number of values. In our example, the average is 8.3 (2+5+7+10+12+14=50, which is divided by 6).

Find the difference between each value and the average. Using our example, the differences are: 2 - 8.3 = 6.3 5 - 8.3 = 3.3 7 - 8.3 = 1.3 10 - 8.3 = 1.7 12 - 8.3 = 3.7 14 - 8.3 = 5.7

Calculate the average of the differences by adding them and dividing by the number of observations. The average of the differences in our example is 3.66: (6.3+3.3+1.3+1.7+3.7+5.7 divided by 6).