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# Statistics – Mean and Median Deviation

## Mean Deviation about the Mean

The AM of the numerical deviations of the observations from the mean of the data is called the mean deviation about the mean.

## Mean Deviation about the Median

The AM of the numerical deviations of the observations from the median of the data is called the mean deviation about the median.
Let x1, x2, x3,…xn be the given observations. Let x be the AM and M be the median. Then,

The formula to calculate Mean deviation is as stated below:

where,

## How to Calculate Mean Deviation?

Example: Find the mean deviation about  the mean for the following data: 15, 17, 10, 13, 7, 18, 9, 6, 14, 11

Solution: n = 10

Mean, x¯= (15+17+10+ 13+7+18+9+6+14+11)/10

= 120/10

= 12

The value of (x i – x¯)

3, 5, -2, 1, -5, 6, -3, -6, 2, -1.

So The value of  |x i – x¯|

3, 5, 2, 1, 5, 6, 3, 6, 2, 1.

MD = ∑ |x i -x¯|/n

MD = 34/10

MD = 3.4