The average deviation is a calculation that gives information concerning how much certain values differ from the mean value. Average deviation is sometimes used instead of standard deviation because it is simpler to calculate. This type of calculation is useful in mathematical fields such as statistics. You also might be required to find the average deviation in a middle school, high school or college math class.

List a set of values.

Add the values and divide the total by the number of values present to calculate the average value. For instance, if you have 10, 15, 17 and 20, you would add these numbers to get 62. You would then divide 62 by 4 to get an average value of 15.5.

Subtract your answer from Step 2 from the first value in the list to find the deviation for this value. For example, you would subtract 15.5 from 10 to get -5.5. State your answer as an absolute value, which means that there will not be a negative or positive sign. Therefore, -5.5. would become 5.5.

Repeat Step 3 for the other values in the list to find their deviations. In this example, you would have the following deviations: 0.5, 1.5 and 4.5.

Add the deviations from Steps 3 and 4 and divide the total by the number of values that you added to find the average deviation. For this particular problem, you would add 0.5, 1.5, 4.5 and 5.5 to get 12. You would then divide 12 by 4 to get an average deviation of 3.