Question

What deviation means?

Answer 1

Deviation:

Deviation, in statistics, is the difference between the expected value and the observed value. Mean deviation is denoted by $\sigma$

It can also be defined as the square root of variance.

The formula to calculate the mean deviation for ungrouped data is $\mathit{\sigma }\mathbf{=}\sqrt{\frac{{\displaystyle \sum _{i=1}^N{\left(x_i-\overline{X}\right)}^2}}{\mathbf{N}}}$where $x_i$ is the value of the $i^{th}$ element, $\overline{X}$ is the mean of the data, and $N$is the size of the population.

The formula to calculate the mean deviation for grouped data is $\mathit{\sigma }\mathbf{=}\sqrt{\frac{{\displaystyle \sum _{i=1}^N{f}_i{\left(x_i-\overline{X}\right)}^2}}{\mathbf{N}}}$, where $x_i$ is the value of the $i^{th}$ element, $f_i$ is the frequency of the $i^{th}$ element, $\overline{X}$ is the mean of the data, and $N$is the size of the population.