**1. Introduction**

The analytic hierarchy process (AHP) is widely used in multi-criteria decision-making tool for tackling multi-attribute decision-making problems in real situations [1]. It represents a powerful technique for solving complicated and unstructured problems that may have interactions and correlations among different objectives and goals [2]. The AHP helps the decision makers to organise the critical aspects of a problem into a hierarchical structure similar to a family tree [3]. It is based on experts' judgements through pairwise comparisons. Experts are interviewed and pairwise comparison judgements are applied to pairs of homogenous criteria, eventually generating the overall priorities for ranking the alternatives [1].

AHP gained substantial attention as a possible solution to the decision-making problems in different organisational areas, for example, the selection of maintenance policy or factors of employee suggestion schemes which will be more deeply illustrated in the following section. However, this method can also be utilised in many other fields. For example, in the study [4], the fuzzy AHP was employed to prioritise and select a suitable organisational structure. The AHP method has been widely used in the decision-making problems that involve multiple criteria in multiple levels [5] as well. The method helps to decompose their decision problem into hierarchy of factors, each of which can be analysed independently and once the hierarchy is built, the decision makers systematically evaluate its various elements by comparing them one to another, two at a time, with respect to their impact on an element above them in the hierarchy [6]. AHP method is used to measure the importance of these factors.

Moreover, this technique allows for the search of relative importance placed on product attributes and attribute levels of the analysed complex goods [7]. To make the pairwise comparisons, we need a scale of numbers that indicate how many times a more important or dominant element over another element was, with respect to the criterion or property, with respect to which they are, compared [8].

In this chapter two case studies are presented: first, empirical case study will be utilised to evaluate and select the most appropriate maintenance approach; the second one, based on expert opinion will present a possibility to formalise the importance levels for the importance of factors of sustainability of employee suggestion schemes.
