*2.5. Variance Threshold*

This method is used to identify features with variance. The features eliminated based on variance are those with zero value, near to zero value, or below a specific threshold [49–51].

The variability in a group given with {*x*1, *x*2, *x*3, ..., *xn*} is the standard error; in other words, it is the difference between the samples and the average value of the group *x*, as in Equation (4) [52].

$$
\sigma^2 = \frac{\sum\_{i=1}^n \left(\mathbf{x}\_i - \overline{\mathbf{x}}\right)^2}{n-1} \tag{4}
$$
