*3.1. Database Filtering for Outlier Values and Noise Removal*

A relatively simple filter to remove outlier values was constructed. The limit of the outlier value was stated at six times the mean value. First, 25 outlier values in each database were double-checked and manually confirmed [14,22,23].

$$
\varepsilon(\mathbf{x}) = \overline{\mathbf{x}} \text{ of } \mathbf{x}\_0; \text{ if } \varepsilon(\mathbf{x}) \ge \overline{\mathbf{x}} \text{ (} \mathbf{6}m\text{), } \mathbf{x} = m \tag{1}
$$

where:

*x* is the actual value, *m* is the mean value.
