## 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 x_{1}, x_{2}, x_{3},…x_{n} 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**