*2.1. Analytic Hierarchy Process (AHP) Method*

The AHP method is the most frequently used in practice among all the subjective methods for the evaluation of criteria weights. The reason is that this method is mathematically substantiated, logically understandable, and allows the performance of a quantitative determination of the consistency of the evaluations provided by each of the experts. The experts compare all the possible pairs of criteria with each other. The pairwise comparison matrix *P* = *pij* is theoretically a ratio of unknown criteria weights: *pij* = *wi wj* , (*i*, *j* = 1, 2, . . . , *m*), *pij* = <sup>1</sup> *pji* , *pii* = 1, where *m* is the number of criteria. The element *pij* shows by how many times the *i*-th criterion is more important than the *j*-th one. The scale 1-3-5-7-9 suggested by the author of the method—Saaty [2]—is applied to the evaluation.

The criteria weights *ω* are the normalized values of the eigenvector of the matrix *P*, corresponding to the largest eigenvalue *λmax* of the matrix:

$$P\overline{\omega} = \lambda \overline{\omega} \tag{1}$$

The degree of consistency (internal consistency) of the expert evaluations determines the Consistency Index *CI* and the Consistency Ratio *CR*:

$$CI = \frac{\lambda\_{\max} - m}{m - 1},\tag{2}$$

$$CR = \frac{CI}{RI'} \tag{3}$$

where *RI* is the average evaluation of the *CI* of the simulated matrices of the order of *m* [2]. The evaluations are considered to be consistent if the Consistency Ratio is such that *CR* < 0.1.
