Recent years have seen an increase in the importance of assessing the environmental and social impacts of industrial product supply chains, leading to the introduction of the concept of supplier sustainability, which entails meeting all suppliers' economic, environmental, and social needs. Typically, supplier selection decisions are based on expert opinions presented as supplier scores. Experts may not be equally familiar with all aspects of suppliers' economic, social, and environmental attributes when evaluating sustainability metrics. The purpose of this paper is to present a new approach for selecting a sustainable supplier using the COPRAS (Complex Proportional Assessment) multicriteria group decision-making process. Suppliers' scores and the weights of each criterion are expressed verbally by experts, by using linguistic variables. Then the linguistic terms are transformed into equivalent type 2 fuzzy numbers. Using fuzzy type 2 numbers facilitates aggregating experts' opinions during group decision-making. The proposed approach assumes that the problem analyst, in addition to collecting the suppliers' scores given by the experts, also determines a degree of expertise for each expert in each criterion and aggregates the data by the COPRAS method to determine the optimal decision. The analyst's verbal variables to represent his view on the validity of each expert are then converted into intuitionistic fuzzy numbers. Intuitionistic fuzzy numbers provide the possibility of presenting uncertainty and doubt from the analysts' point of view. This paper illustrates the application of the model by presenting an example and discussing its results.
