Valuable information for decision-making can be obtained by collecting and analyzing opinions from diverse stakeholder or respondent groups, which usually have different backgrounds and are variously affected by the topics under survey. For this to succeed, it is necessary to manage the uncertainty of respondents’ opinions, different number of filled questionnaires among groups, different number of questions for each stakeholder group, and relevance of subsets of respondent groups. This work proposes handling the hesitance of respondents’ opinions for the rating scale questions. To evaluate the collected opinions, a three-level aggregation model is developed. In the first level, the overall opinion of each respondent is computed as a mean of fuzzy numbers covering uncertain answers and their respective hesitance. In the second level, stakeholder groups are considered as a whole. Aggregation by a relative quantifier is applied to calculate the validity of a proposition the majority of respondents have a positive or negative opinion. At the third level, the consensus among diverse subsets of stakeholder groups is calculated considering the relevance of each group independently as well as their so-called coalitions by Choquet integral. Finally, the proposed model is illustrated by a real-life case study.

Environmental policy in the European Union is a hot topic for both practitioners and researchers. Their interests are attracted mainly by the main tool of this policy—emissions trading within the EU ETS. In literature focusing on the impacts of the EU ETS, the EU is usually considered to be a compact unit and its structure is omitted there. In particular, the impacts on a single company (regardless its geographical location), on a sector of industry (regardless the member countries), or on some subset of the involved companies with respect to non-EU competitors are often explored. However, through the eyes of national governments, it is vital for the countries to keep their national industrial sectors competitive not only against companies from countries outside the EU but also from other EU countries. This paper focuses on the influence of the EU ETS on the national steel sectors in the EU and their competitiveness. The hybrid PROMETHEE-DEA approach is used to assess how the price of emission allowance and grandfathering within the EU ETS impact the technical efficiency and competitiveness of these national sectors. The results of this study show that the volatile allowance price influences the efficiency and grandfathering affects the competitiveness of the EU national steel sectors.