It is also known as the mean absolute deviation and represents the mean of the absolute deviations of the observations from the suitable average which may be the arithmetic mean, the median or the mode.

Formulas to calculate Mean deviation as stated below:

Here, 

denotes the summation.

X = Observations 

 = Mean

\N = Number of observations

M = Median

In frequency distribution, the mean deviation is given by 

When the mean deviation is calculated around the median, then its expression becomes

The mean deviation around the mode is

For data population, the mean deviation around the population mean 𝛍 is:

Solved Example

Q1: Anubhav scored 85, 91, 88, 78, 85 for a series of exams. Calculate the mean deviation for his test scores.

Ans:  Given test score; 85, 91, 88, 78, 85 

Mean

Now subtract mean from each number

Mean deviation = 16.4/5 = 3.28

Thus we can say that on average the student's test scores vary by a deviation of 3.28 points from the mean.

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