Mean Deviation
The mean deviation is the first measure of dispersion that we will use that actually uses each data value in its computation. It is the mean of the distances between each value and the mean. It gives us an idea of how spread out from the center the set of values is.
Here's the formula.
A student took 5 exams in a class and had scores of 92, 75, 95, 90, and 98. Find the mean deviation for her test scores.
First find the mean.
Now subtract the mean from each score, take the absolute value of each difference, total the absolute values, then divide by the number of values. A column approach works well here.
So, 
. We can say that on the average, this student's test scores deviated by 6 points from the mean.
The mean deviation is the first measure of dispersion that we will use that actually uses each data value in its computation. It is the mean of the distances between each value and the mean. It gives us an idea of how spread out from the center the set of values is.
Here's the formula.
First find the mean.
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. We can say that on the average, this student's test scores deviated by 6 points from the mean.