Mean Absolute Deviation

$$\mathrm{MAD}\left(X=\left\{x_1,x_2,\dots ,x_n\right\}\right)=\frac{1}{n}\sum _{i=1}^n\left|x_i-\bar{x}\right|$$

where $\bar{x}=\frac{1}{n}{\sum }_{i=1}^n{x}_i$, thus $z_i=\frac{x_i-\bar{x}}{\sqrt{\frac{1}{n}{\sum }_{i=1}^n{\left(x_i-\bar{x}\right)}^2}}$

Median Absolut Deviation

Robust against Outliers.