You find the mean absolute deviation by first finding the mean, and then subtracting all the values in the data set from that, creating a new data set, and then you find the mean of this new data set.
Example:
3, 2, 5, 9, 4
Mean(add them all, divide by how many there are): (3 + 2 + 5 + 9 + 4)/5 = 4.6
Subtract 4.6 from/to all the values:
4.6 - 3 = 1.6
4.6 - 2 = 2.6
5 - 4.6 = 0.4
9 - 4.6 = 4.4
4.6 - 4 = 0.6
Find the mean of these values:
(1.6 + 2.6 + 0.4 + 4.4 + 0.6)/5 = 1.92
So the mean absolute deviation is 1.92.
