## 5 Discussion  
Considering the aforementioned findings, useful conclusions can be drawn. Firstly, there is an increasing trend of MCDA publications on environmental decision-making issues. Most of the reviewed literature supports the growing popularity of MCDA in tackling environmental issues. Many authors consider this approach a necessary tool, and it is often described as effective, flexible, useful, and suitable. The significance of MCDA is highlighted by the increasing number of publications studying it, particularly in the last decade. Out of the 80 review papers selected, the majority were published after 2010, with only 10 published between 2000 and 2010 and 70 published between 2011 and 2023. Many review papers show that MCDA combined with fuzzy sets is commonly used. Out of 25 papers, 23 report using the fuzzy approach, and 2 exclusively focus on it. There is also an increase in the use of hybrid MCDA. There is a challenge for decision-makers when selecting the most suitable MCDA technique, as each method can result in varying alternative rankings. The hybrid MCDA, which can incorporate multiple methods, such as combining MCDA methods, fuzzy approaches, or life cycle analyses, can lead to more satisfactory results. Additionally, it allows for the inclusion of both objective and subjective criteria importance in the utility function value. It is important to note that the parallel application of fuzzy logic can manage the increased uncertainty caused by human judgement and imperfect preference relations. This brings the decision-making process closer to real-world conditions. In terms of preferred MCDA methods, AHP is either the main or one of the main methods in 68 of the 80 papers reviewed. TOPSIS is mentioned 16 times, ANP is mentioned 12 times, and PROMETHEE is mentioned 11 times. AHP is widely recognised for its simplicity and user-friendliness, making it convenient for decision-makers. It is highly likely that decision-makers are inclined towards employing methods that scientists have thoroughly tested to guarantee the reliability of the findings. It is important for the decision-maker to carefully evaluate which MCDA method is most suitable for the specific problem at hand, as each method has its own strengths and weaknesses. In relation to nations showing an increasing interest in the use of MCDA for environmental decision making, 38 review papers did not provide any clear conclusions. However, from the remaining 42 papers, certain countries were identified as more prominent. Furthermore, some papers highlighted more than one leading country, resulting in a more comprehensive assessment. China is the country with the highest number of mentions (22), followed by Iran (14), Turkey, and the USA (12 each). India is mentioned nine times, while Greece and Spain are each mentioned seven times. These results illustrate the increasing interest in using MCDA methods, with Asia showing a significant inclination and several European nations also adopting these techniques. Sensitivity analysis determines whether the ranking of alternatives is robust or shows increased sensitivity to changes in parameter values. Despite its importance, sensitivity analysis is not widely applied in the 80 review papers that were studied. Only three of the reviewed papers placed strong emphasis on its significance: [PERSON] and [PERSON] (2018), [PERSON] and [PERSON] (2018), and [PERSON] et al. (2018). Of the review papers, 65% do not reference sensitivity analysis. However, a small number of papers (three) strongly emphasised its importance. Ultimately, decision-makers who do not use sensitivity analysis may be unaware of its benefits or undervalue its role in the decision-making process. Alternatively, they may require more complex probabilistic and fuzzy frameworks to deal with increased levels of uncertainty, as identified by [PERSON] et al. (2018).