How far, on average, all values are from the arithmetic mean of the data set.
To calculate it:
• find the mean of all values
• calculate the distance of each value from that mean (the "absolute deviation")
• then find the mean of all those distances!
Example: 4, 6, 8:
* Mean = (4 + 6 + 8) / 3 = 6
* Absolute Deviations = |4-6|, |6-6|, |8-6| which gets us 2, 0, 2
* Mean Deviation = (2 + 0 + 2) / 3 = 1.333...
(Also called Average Deviation)
See: Arithmetic Mean