Thus, the first contribution of this research is to determine the importance and applicability of sustainable attributes through a questionnaire-based survey as a systematic method. Furthermore, the literature shows that the relative weights of sustainability criteria were not considered in most methods (Singh et al., 2015b). However, Wang et al. (2008) stated that attribute weights and alternatives calculated by this method are invalid.
The company's suppliers are assessed on the basis of the established characteristics (in the first objective of this study). Some of the most recent research related to supplier selection is listed in this section. The model not only evaluated the performance of the suppliers, but also maintained the consistency level of the assessment.
In that research, the criteria weight and the ranking of the suppliers were obtained with the help of FANP. One of the main challenges in the supplier evaluation process is choosing the right criteria. The first subsection deals with the questionnaire-based survey to establish the importance and applicability of the criteria and their corresponding sub-criteria.
In this study, the following sub-criteria were used for material, price of the supplied material, etc.
The attributes of the environmental aspect
Environmental Management System (Env.M.S) : A factor that shows the supplier's effort in environmental management (Tseng, 2011). Green warehousing ( : This indicates the supplier's effort to reduce costs and increase social responsibility by storing raw materials and, in general, all necessary materials for companies based on the consideration of the carbon footprint (Rostamzadeh et al., 2015). Eco-design ( : This measures the supplier's effort for the implementation of activities aimed at reducing the impact of products on the environment throughout their entire life cycle (Rostamzadeh et al.
The use of a modern ecologically efficient transport fleet, such as energy-efficient vessels and high Euro standards for trucks ( ) Rostamzadeh et al. The use of low-sulfur green fuels and alternative fuels such as liquefied natural gas ( ) Rostamzadeh et al. Green technology ( : A factor that shows the supplier's effort in producing green products (Lee et al., 2009).
Materials used in Supplied Components that reduce the impact on natural resources ( ) Kannan et al. The ability to change the process and product to reduce the impact on natural resources ( ) (Li et al.
The attributes of the social aspect
Green transportation ( ): This factor shows the supplier's effort to minimize the environmental pollution while transferring the necessary order.
Questionnaire development
It is worth noting that after collecting the dataset, the reliability test was performed to ensure that the instrument and collected data were reliable for further analysis. According to the literature, Cronbach's alpha is the most commonly used test to demonstrate the internal reliability of indicators for a specific scale. The test was conducted in two phases; the first phase was testing the reliability of the importance of the dataset and the second phase was conducted to test the reliability of the applicability of the dataset.
Regarding the importance of the data set, the results of running an internal reliability assessment test with Cronbach's alpha revealed that all the 13 criteria had an alpha value higher than the recommended value of 0.70 as suggested by Ferketich (1990). Another statistical analysis, the Mann-Whitney U test, was performed to assess whether the mean scores for the two sets of data (importance and usefulness) differed significantly. Since the Mann-Whitney U test is performed on ranked scores, the data for the two groups need not be normally distributed Olugu et al.
All the main measures of the three aspects were evaluated by this test and the p-value of each of them was greater than 0.05 (a p-value less than 0.05 means that there is a significant difference between the data sets). The results show that there is no significant difference between the mean scores of the two data sets. Therefore, we can say that there is a strong correlation between the importance and usefulness of the listed criteria.
The proposed FPP-FTOPSIS
Fuzzy TOPSIS (FTOPSIS)
It is based on this concept that the best alternative must have both the smallest distance from the Positive Ideal Solution (PIS) and the longest distance from the Negative Ideal Solution (NIS) at the same time. In this step, the aim is to evaluate the alternatives with respect to each sub-criterion. It is represented by R. Create a weighted normalized matrix by multiplying the normalized matrix by the weights of the criteria. . , where and is the weight of the jth attribute obtained by FPP in this study).
Alternative is closer to the FPIS and further from FNIS as approaches to 1 Kannan et al. In the case of group decision making, the importance weights need to be aggregated to achieve a single fuzzy number for each weight. In this research, the fuzzy numbers are aggregated by the arithmetic mean operator Singh et al.
Where d is the number of decision makers (DM) and represents the idea of kth DM for the relative weight of criterion i. Where d is the number of decision makers (DM) and represents the idea of kth DM for evaluating the performance of the organization based on the i-th criterion. In the first step, using Table 3, the opinions of the decision-makers are collected, as a pairwise comparison, and using equation (21) the aggregated fuzzy comparison matrix for the aspects, criteria and sub-criteria is obtained.
In the second step, the sharp weight of each sub-criterion is calculated using FPP. It is worth noting that the local weight of each aspect, criterion and sub-criterion is first calculated, after which the global weights of the sub-criterion are derived by multiplying the local weight of each aspect by the local weight of its criterion and the local weight of the related sub-criterion, the global weights of the sub-criterion are derived. For example, Economic aspect (local weight is 0.2), quality (local weight is 0.3) is one of the criteria in economic aspect and rejection rate is one of the sub-criteria of quality (local weight is 0.3).
In the third step, an aggregated (Equation 22) fuzzy decision matrix is generated based on the opinion of the decision makers using a table of linguistic variables (Table 4).
Case study and Results
Criteria for sustainable supplier selection and weigh calculation
Lastly, the ranking is done by FTOPSIS. management in textile engineering) (each of them has more than 15 years of experience in the textile industry) from the case company were asked to express their opinion (as FAHP-FPP comparison matrix) on the aspect and criteria based on Table 3 Then, using the summation method (Equation 21), the final comparison matrix of each of them is obtained. In the second step, the optimal weight (global weight) of each sub-criterion should be calculated using FPP.
It is worth noting that experts were asked to reassess their opinions regarding the inconsistency. Since the numbers below the diagonal are the reverse of the numbers above the diagonal, these numbers are not represented here. After collecting the combined comparison matrix, the exact weights of aspects and criteria (local weight) were calculated using FPP6.
Then the local weight and the global weight of each sub-criterion were calculated (see Table 5).
Evaluating the suppliers by FTOPSIS
Table 7. The aggregated data set
- Validation of the model
- Consistency index
- Comparing with TOPSIS
- Sensitivity analysis
- Result analysis of the developed MCDM model
- Managerial implication
- Conclusion
In general, the ranking of suppliers is made in relation to 46 sustainability sub-criteria. In this part, the results obtained from the proposed method were compared with the results of classical TOPSIS (as one of the best techniques in decision making (Ertuğrul et al., 2008)). In this phase, FPP as a new fuzzy programming method was used to calculate the weight of the attributes.
Finally, FTOPSIS as one of the most used MCDM techniques was applied to rank the alternatives. Company executives were asked to provide their opinions regarding the weights (Tables D1-D7) and performance of the attributes (Table 4). The proposed model was implemented in a real textile company and the company's best suppliers were evaluated based on 13 criteria and 46 relevant sub-criteria defined in the first objective.
The results for the supplier assessment can be effective in increasing the quality of the product, reducing the cost and toxic material in the supply chain, and increasing the rate of sale of the product. A questionnaire was developed to evaluate the importance and applicability of the criteria and sub-criteria with the help of experts from academia and industry. Consequently, an average mean value was obtained for each of the criteria to show their level of importance and applicability.
Comparative study of green supplier selection of the US, Japanese and Taiwanese electronics industries in China. Applying environmental criteria to supplier assessment: A study in the application of the analytic hierarchy process. This characteristic is counted as a disadvantage because customer satisfaction decreases with increased rejection rate of the product.
Degree of flexibility of the supplier in changing the orders based on the customer's request. Ability of the supplier's R&D to meet the company's current and future demand. This factor helps to improve the quality of the existing products and to reduce hazardous materials in the design.
Supplier's ability to change process and product design to reduce impact on natural resources (Kannan et al., 2015). The opinions of the two experts The aggregated dataset Economic Environment Social Economic Environment Social.
