A hyper-hybrid fuzzy decision-making framework for the sustainable-resilient supplier selection problem: a case study of Malaysian Palm oil industry.

One of the major challenges of the supply chain managers is to select the best suppliers among all possible ones for their business. Although the research on the supplier selection with regards to green, sustainability or resiliency criteria has been contributed by many papers, simultaneous consideration of these criteria in a fuzzy environment is rarely studied. Hence, this study proposes a fuzzy decision framework to investigate the sustainable-resilient supplier selection problem for a real case study of palm oil industry in Malaysia. Firstly, the resilient-based sustainable criteria are localized for the suppliers' performance evaluation in palm oil industry of Malaysia. Accordingly, 30 criteria in three different aspects (i.e. general, sustainable and resilient) are determined by statistical tests. Moreover, a hyper-hybrid model with the use of FDEMATEL (fuzzy decision-making trial and evaluation laboratory), FBWM (fuzzy best worst method), FANP (fuzzy analytical network process) and FIS (fuzzy inference system), simultaneously is developed to employ their merits in an efficient way. In this framework, regarding the outset, the relationships among the criteria/sub-criteria are obtained by FDEMATEL method. Then, initial weights of the criteria/sub-criteria are measured by FBWM method. Next, the final weights of criteria/sub-criteria considering the interrelationships are calculated by FANP. Finally, the performance of the suppliers is evaluated by FIS method. To show the applicability of this hybrid decision-making framework, an industrial case of palm oil in Malaysia is presented. The findings indicate the high performance of the proposed framework in this concept and identify the most important criteria including the cost in general aspects, resource consumption as the most crucial sustainable criterion and agility as the most important resilient criterion.

Introduction

Over the past 20 years, the supply chain management problem has become one of the most popular issues among researchers due to its role in increasing the efficiency and profits of companies and organizations (Fallahpour et al. 2017). In this field, one of the most important branches of supply chain management is the supplier selection problem (Fallahpour et al. 2017). This problem attempts to select best suppliers among potential suppliers. In the traditional studies, researchers only considered the general aspects of the supplier selection problem (i.e. price, quality, delivery and service), but by increasing concerns about the environmental issues, scholars incorporated the environmental aspects in the problem that leads to emerging the green supplier selection problem. Then, the social impacts were added to the problem that resulted in developing the sustainable supplier selection problem. Based on Fallahpour et al. (2017), the supplier selection problem is a critical strategic decision and the multi-criteria decision-making (MCDM) methods can help the decision makers in evaluating the suppliers’ performance based on the related criteria.

In general, when the economic, environmental and social aspects are simultaneously considered, the traditional supply chain converts to a sustainable one. In the two last decades, supply chain managers have given more attention to sustainability to mitigate the effects of their activities on environment, improve their long-term relationship, as well as increase their end-customer satisfaction in their supply chain (Amindoust 2018; Stević et al. 2020; Vieira et al. 2020). In this regard, many researchers stated that evaluation of suppliers’ performance, as the paramount part of the upstream of supply chain, according to economic and environmental criteria along with social criteria (sustainability criteria), is the key issue in improving the concept of sustainability in a supply chain (Chen et al. 2020; Fallahpour et al. 2017; Jain and Singh 2020; Kannan 2018; Vahidi et al. 2018).

One of the important concepts that attracted the attention of the researchers in recent years is “resiliency”. In general, resilience is the ability of the supply chain to recoil from disruptions. Thunderstorms on the 17th of March, 2000, at Albuquerque, New Mexico, cause a fire in Philips semiconductor manufacturing plant that was Nokia’s and Ericsson’s only cellphone chip supplier. Nokia reacted very quickly and set up an alternative scenario to address this disruption. On the other hand, it took 6 weeks for Ericsson to plan for dealing with the problem, leaving it unable to find a replacement for its chips’ supplier. This disruption and inability to deal quickly with it caused the company to lose its market share, mainly to Nokia, so that Ericsson announced the cessation of its mobile product line 2001 (Zsidisin and Wagner 2010). This example shows the importance of resilience in the supplier selection problem. Many reasons cause disruptions in sustainable supply chains such as terrorism, natural disaster (flood, tsunamis, earth quick, fire, etc.), pandemic diseases (e.g. COVID 19) and so on. These problems have negative influence on different parts of manufacturing systems such as income, efficiency, product quality and competitiveness. So, due to the mentioned reasons, focusing on resilience is absolutely necessary for industries. However, traditional sustainable supplier selection process just includes sustainability criteria and the resilient attributes have been neglected by purchasing managers (Amindoust 2018; Mohammed et al. 2020). For example, Torabi et al. (2015) mentioned that resilience is a kind of management for recognizing the potential disruptions, increasing the ability to control these specified problems and back to the normal conditions. There are examples of lack of focus on resilience which caused big problems for the companies such as company Apple in Japan’s earthquake in 2011 (News 2011). Moreover, it has been reported that neglecting this issue has recently affected other industries in UK and USA (Mohammed et al. 2020). Thus, providing a resilient supply chain can help industries to be safe from disruptions (Sáenz et al. 2018). Suppliers are the main part for integrating resiliency with sustainability in a supply chain. Therefore, developing an applicable decision-making model for evaluating the suppliers’ sustainability performance covering the resilience is a necessity for the decision makers of manufacturing industries.

Despite the dramatic importance of sustainability and resiliency in the supplier selection problem, the combination of these concepts in the context of supplier selection is rare. Owing to the importance of the aforementioned features, developing a model to evaluate the sustainable and resilient performances of the suppliers seems necessary to help the decision makers to make the right decisions. In this regard, there are many studies in the area of sustainable supplier selection such as Gören (2018), Kannan (2018); Liu et al. (2020), Luthra et al. (2017), Memari et al. (2019), Tavana et al. (2017), Vahidi et al. (2018) and Zandieh and Aslani (2019), but there is a lack of conducting a research focusing on resilient-based sustainability (RS) criteria as well as developing an applicable model for performance evaluation. In addition, in the previous resilient-based supplier selection investigations, determining weight of the criteria considering interrelationships between criteria has been ignored by researchers. Furthermore, researchers have always applied those MCDM (even under fuzzy environment) techniques which compute the relative performance of supplier such as analytic hierarchy process (AHP or fuzzy AHP), technique for order of preference by similarity to ideal solution (TOPSIS or fuzzy TOPSIS), decision-making trial and evaluation laboratory (DEMATEL or fuzzy DEMATEL), data envelopment analysis (DEA or fuzzy DEA), analytic network process (ANP), etc. It means these methods do not enable the decision makers to study the performance of suppliers separately. In fact, the above-mentioned models absolutely need a complete data set (called as decision matrix) in their first step, and if this decision matrix is changed, the performance value of each supplier (alternative) will be changed. Moreover, if a new supplier (alternative) is added to the decision matrix, the values of the suppliers’ performance will be changed (as these techniques calculate the relative performance, not the absolute performance).

This study aims at proposing a decision-making framework to determine the most important and applicable RS criteria and assessing suppliers by integrating MCDM methods under fuzzy environment. In the first phase of the proposed model, a list of RS criteria is provided based on the literature and the opinions of the experts (managers of the company). Then, their importance and applicability are measured using statistical tests (parametric/non-parametric tests). In the second phase, interrelationships between criteria (general, resilient and sustainable) as well as the interrelationships between the sub-criteria are determined applying the fuzzy DEMATEL method. Afterwards, the initial weight of each criterion is calculated using the fuzzy best worst method (fuzzy BWM). As selecting the best and the worst criteria is hard task especially when decision makers have different point of view, this study applies the obtained results by FDEMATEL to determine the best and the worst criteria. Then, according to the relationships derived from fuzzy DEMATEL and the results obtained from fuzzy BWM, the final weight of each criterion is computed using fuzzy ANP. Finally, in the last phase, a fuzzy logic-based system, for computing the suppliers’ absolute performance, is proposed using fuzzy inference system (FIS). Indeed, the FIS does not need a complete data set (as the decision matrix) and unlike other indicated techniques can calculate the suppliers’ performance one by one. In the current study, the case study is the palm oil industry of Malaysia (as one of the main industries in Malaysia). Malaysian palm oil industry has very big portion in supplying the total biomass and is considered as the main alternative for renewable energies (Tapia and Samsatli 2020). On the other hand, the generated waste from this industry is of the main concerns of the Malaysian government (Loh and Choo 2013). Moreover, this industry is one of the main producers of carbon emission in Malaysia (Marwanto et al. 2019). Therefore, palm oil companies in Malaysia need to move towards resilient-sustainable and this study presents a suitable model for this transition. Overall, this research contributes to the following:

Developing a new integrated multi stage fuzzy rule-based decision-making system (we call it as hyper-hybrid fuzzy decision-making framework (HHFDMF)) for the first time to evaluate suppliers’ performance according to RS criteria, where weights of the criteria are computed via integrating fuzzy DEMATEL, fuzzy BWM and fuzzy ANP and the performance of each supplier is evaluated via FIS.

Ease the understanding of the resilience concept in the palm oil industry.

Hybridize resilient criteria with sustainability attributes for evaluating and selecting sustainable suppliers.

Localizing the evaluative resilient-sustainable criteria for suppliers’ performance evaluation in the Malaysian palm oil industry.

Having an overview of the graphical illustration of the proposed HHFDMF, Fig. 1 explains the main stages of this research methodology.

Fig. 1

The stages of the proposed hyper-hybrid fuzzy decision-making framework

The rest of this study is organized as follows. The literature is reviewed in “Literature review”. The methodology of research is presented in “Methodology”. “Case study and computational results” presents case study and the obtained results. “Validation of the proposed model” verifies the validity of the model. Then, “Findings and discussion” presents the implication of the study. Finally, “Conclusions, limitations and future work” is dedicated to providing conclusions and future suggestions.

Literature review

Related works

Integration of resilience and sustainable supplier selection is a very new issue in the area of suppliers’ performance evaluation and selection. However, many investigations have been conducted in sustainable supplier selection such as Fathollahi-Fard et al. (2020), Kannan et al. (2020), Liu et al. (2020) and Luthra et al. (2017). There are two main steps in the procedure of sustainable suppliers’ performance evaluation in all the related studies including: (i) determining the suitable criteria for assessing suppliers’ performance and (ii) developing a method for calculating suppliers’ performance according to the specified attributes.

There are many different criteria for evaluating suppliers in the literature. Initially, the economic attributes were used for assessing and ranking suppliers in industries such as quality, flexibility, delivery, etc. (Weber 1991). However, with the increase pressure from the government and the consumers, the new aspects were used along with the economic aspect known as environmental and social aspects. In the related literature, the process of selecting suitable supplier(s) based on these three aspects is called sustainable supplier selection. There are many researches in which sustainability criteria used for supplier selection. For example, Ghadimi and Heavey (2014) collected and sorted the most proper sustainability indicators/attributes for evaluating suppliers’ performance of the medical industry. In another research, Fallahpour et al. (2017) developed a comprehensive list of sustainability criteria for assessing suppliers’ performance based on the three aspects. They introduced new social criteria to the existing sustainability criteria such as standard working hours, overtime pay, workers’ contract, attention to religious and cultural issues at work, etc. They resulted that still economic-based criteria have the maximum influence on the suppliers’ performance. Amindoust and Saghafinia (2017) utilized different sustainability criteria for assessing suppliers’ performance in the textile industry such as price, deliver, environmental management system, inventory level reduction, quality, pollution control, labor health and work safety and social equities. Stević et al. (2020) developed a new MCDM model to the supplier selection problem for a healthcare industry in Bosnia and Herzegovina considering sustainable development criterion. They conducted the sensitivity analysis to show the validation of their proposed model. Hendiani et al. (2020a) studied the supplier selection with sustainability triple bottom line criteria applying a likelihood-based multi-criteria approach considering complex information in type 2 fuzzy environment. The authors showed the application of their model with implementing in a real case study. Jain and Singh (2020) investigated the supplier selection problem considering sustainable development dimensions under must-be criteria using the FIS method. They selected a real case study at the iron and steel industry in India to show the performance of the proposed framework. Chen et al. (2020) developed an integrated rough-fuzzy TOPSIS-DEMATEL to investigate the sustainable supplier selection problem under external and internal uncertainty for smart supply chains. They showed the application of their method in vehicle transmission supplier selection case. Hendiani et al. (2020b) studied the supplier selection problem considering sustainability triple bottom line factors. They extended the fuzzy best-worst method to obtain the weights of the criteria. Also, considering a real case study, the authors employed the graded mean integration representation method to prioritize the suppliers. Negash et al. (2020) examined the sustainable supplier selection applying the Monte Carlo simulation approach considering product quality. The authors showed the model applicability by implementing in a real-life case study. Ecer and Pamucar (2020) combined the fuzzy best-worst method and fuzzy CoCoSo with Bonferroni to investigate the supplier selection problem considering sustainable development dimensions. They selected a real case study in home appliance manufacturer in Serbia to illustrate the application of the proposed framework. Jia et al. (2020) studied the sustainable supplier selection and order allocation problem applying tractable approximation and robust goal programming model. They selected a real case study in a steel company to show the performance of the proposed model. Tirkolaee et al. (2020) proposed a mixed model based on multi-objective programming and fuzzy decision making to sustainable-reliable supplier selection in the supply chain network design problem. The authors applied integrated DEMATE-ANP-TOPSIS to select the best suppliers and used weighted goal programming to solve the multi-objective mathematical model.

Recently, the issue of resiliency has been integrated to the field of sustainable supplier selection. Thus, new aspect with its corresponding criteria has been included to this process. As an example, Vahidi et al. (2018) developed a list of resilient-sustainable evaluative criteria for assessing suppliers. In this research, the most appropriate supplier was selected according to the previous research and experts’ opinions. Moreover, Mohammad et al. (2020) developed an integrated model for selecting the best supplier on the basis of resilient-green criteria. Three aspects called traditional, green and resilient with their corresponding criteria were applied for assessing suppliers’ performance. In the traditional aspect, attributes such as price, operating capacity, quality, turnover, lead time and performance history have been applied. In the green aspect, criteria such as waste management, environmental certificate and environment management systems were utilized. In addition, in the resilient aspect, they added visibility to the resilient criteria (including robustness, agility, leanness and flexibility) provided by Purvis et al. (2016) for studying the suppliers’ performance. In addition to these papers, by focusing on the literature, it is seen that there are other papers in supplier selection with the focus on resiliency such as Amindoust (2018), Mitra et al. (2009), Sawik (2013), Haldar et al. (2014) and Parkouhi et al. (2019) that have applied resilient criteria for calculating the performance of the suppliers. In all these researches, criteria are based on merely the previous studies as well as experts’ opinions. However, there is no investigation which focuses on providing a comprehensive list of RS criteria as well as determining their importance and applicability in real-world problems.

The literature reports that there are many models under the name of MCDM in the area of supplier selection (economic-based supplier selection, sustainable-based supplier selection, RS-based supplier selection, etc.). In the recent decades, the majority of the methods are under fuzzy environment or grey environment such as fuzzy AHP, fuzzy TOPSIS, grey DEMATEL, grey SAW (simple additive weighting), etc. For example, Fallahpour et al. (2019) integrated fuzzy preference programming (kind of fuzzy AHP) with fuzzy VIKOR to prioritize the suppliers in the textile industry based on carbon management criteria. First, the weights of the criteria were calculated using fuzzy preference programming. Then, fuzzy VIKOR was performed for selecting the best supplier. In the same way, Mohammed et al. (2020) integrated fuzzy AHP with fuzzy TOPSIS for evaluating suppliers’ performance according to the resilient-green (RG) criteria. In the first step, they applied fuzzy AHP for calculating the weight of the RG criteria. Then, by applying fuzzy TOPSIS, the best supplier was selected. Moreover, an order allocation was conducted. In another investigation, Parkouhi et al. (2019) integrated grey DEMATEL with grey SAW for selecting the most appropriate supplier. After computing the weight of each criterion using grey DEMATEL, the ranking was done by grey SAW. The results showed that customization was known as the most important criterion.

The gaps and contributions

As reported in the literature, the supplier selection problem has attracted the attention of researchers in the last decade. In this regard, many papers investigated the sustainable supplier selection problem. On the other side, resiliency is one of the relatively novel concepts in the supply chain management area, and few papers studied the sustainable-resilient supplier selection problem in recent years. However, the literature on the resilient supplier selection problem is still thin. On the other hand, the simultaneous consideration of the sustainability and resiliency measures in the supplier selection problem is rarely addressed in the related literature especially under the fuzzy environment. Hence, this research attempts to develop a hybrid fuzzy decision framework for studying the mentioned problem. The main contributions of this paper are (i) proposing a hyper-hybrid decision-making framework in which the weights of criteria obtained applying an integrated FDEMATEL-FBWM-FANP and the alternatives (suppliers) are ranked employing FIS and (ii) we investigate the concepts of resilience and sustainability in the palm oil industry. The main advantages of the developed decision-making framework are (a) considering interrelationships between the related criteria/sub-criteria that are ignored in the related literature applying the FDEMATEL, (b) decreasing in the cognitive burden and also drastically increasing in reliability of the results employing FBWM within FANP, (c) the developed two-by-two FIS model provides the absolute performance for each supplier (unlike other models such as FTOPSIS, FDEA, etc. which compute the relative performance), (d) the FIS model is very flexible in adding new criteria for performance evaluation (unlike other methods in which by adding new criteria, all the steps of the model should be re-run (such as FVIKOR, FTOPSIS, FDEA)).

Methodology

In this section, the methodologies that are applied in this research are described, briefly. We assume that the readers are already familiar with some basic concepts of fuzzy set theory like triangular fuzzy numbers and its calculations, crisp numbers, membership functions and linguistic variables. Hence, we do not present this concept in this section, and for further information about fuzzy set theory, membership function and crisp value, refer to Jiang et al. (2020) and Maués et al. (2020). Albeit, it should be noted that we use the graded mean integration representation () for defuzzification of the fuzzy numbers which is defined as follows:

where represents the triangular fuzzy number.

FDEMATEL

DEMATEL is one of the methods to identify interrelationships among factors by using the relationship matrix. Lin and Wu (2008) developed fuzzy DEMATEL (FDEMATEL) which is adapted with fuzzy environment. The steps of FDEMATEL are as follows:

Step 1 :Gathering and evaluating the opinion of the experts about the research problem. In this research, we use linguistic scales in which the corresponding values are given in Table 1.

Table 1

Transformation table of linguistic variables (BaykasoğLu et al. 2013)

Linguistic terms	Linguistic values	Triangular fuzzy numbers
No influence (No)	(1, 1, 1)	1~
Very low influence (VL)	(2, 3, 4)	3~
Low influence (L)	(4, 5, 6)	5~
High influence (H)	(6, 7,8)	7~
Very high influence (VH)	(8, 9,9)	9~

Step 3: Forming a fuzzy matrix based on opinions of the experts. To create this matrix, experts compare the criteria/sub-criteria in pairs based on how much they influence each other (based on Table 1). Suppose that there are p experts and n criteria, so there are p fuzzy matrix (n × n) that the average of these matrices is applied to calculations.

Step 4: Normalizing the fuzzy matrix using the following relations:

Step 5: Determining the total fuzzy matrix. In this step, at first, the inverse of the normalized matrix is calculated. Afterwards, it is subtracted from the matrix I. Eventually, multiply the normal matrix by the resulting matrix. The related relations are given in below.

Step 6: Create and analyze the causal diagram. For this purpose, in the outset, sum of each row, denoted by Di, and sum of the each column, denoted by Ri, are calculated. Di shows amount of effect of factor i on the other factors in the system. On the other side, Ri shows the effectiveness of that factor from other factors of the system. Afterwards, D + R and D − R are calculated. The higher the D + R value, the more interactive it is with other system factors. On the other hand, if D − R is positive, the variable is a causal variable, and if it is negative, it is considered a disability. The causal diagram is depicted based on D + R and D − R. To gain more detail about steps of FDEMATEL, see Lin and Wu (2008). Also, we can define a threshold based on expert opinions for deleting negligible influential flows.

FBWM

Recently, Rezaei (2015) has introduced the best-worst method (BWM) that is an improvement to pair-wise comparison matrix (PCM)-based methods (e.g. AHP and ANP). Guo and Zhao (2017) developed the fuzzy version of the BWM named FBWM with purpose of eliminating the ambiguities of the respondent’s words by applying fuzzy numbers. The steps of the FBWM are explained in below (You et al. 2017). The main advantages of the FBWM over the similar PCM-based methods such as AHP are as follows: (a) the reliability of this method’s output (weights of factors) is high because of low inconsistency in the DM’s opinions as the result of lower pair-wise comparisons, (b) the cognitive burden related to numerous pair-wise comparisons is drastically reduced and (c) this method can be easily combined with other MADM methods.

Step 1: Determining the worst and the best criteria

In the outset, it is needed to determine the best and the worst criteria. In the traditional way, decision makers (DMs) determine these criteria while this is not an easy task especially when there are several DMs and they do not reach a consensus on this case. Hence, in this study, we use the obtained results from FDEMATEL to determine the best and the worst criteria. To do this, criteria with the lowest D+R is considered as the worst criteria and the criteria with the highest D+R is considered as the best one. If some criteria have same D+R, the best/worst criteria should be selected based on the expert opinion.

Step 2: Creating the comparison vectors for the best and the worst criteria

Let c1, …, cn show the related criteria. The triangular fuzzy number is defined as the comparison of the criteria i to criteria j, given in the form of linguistic variables by decision makers. Linguistic variables can be transformed into a triangular fuzzy number using Table 2.

Table 2

Transformation table of linguistic variables (You et al. 2017)

Linguistic terms	Membership function
Equally important (EI)	(1, 1, 1)
Weakly important (WI)	(0.6667, 1, 1.5)
Fairly important (FI)	(1.5, 2, 2.5)
Very important (VI)	(2.5, 3, 3.5)
Absolutely important (AI)	(3.5, 4, 4.5)

Note that denotes the vector of comparison between best-to-others and shows the vector of comparison between others-to-worst.

Step 3: Calculating the optimal weights

By considering , , , and, the optimal weights can be calculated using the non-linear programming model expressed in relation (7).

Step 4: Check the consistency ratio (CR)

In final step, the consistency ratio must be checked. Table 3 shows the consistency index (CI) and the maximum possible value of k∗ for each possible . The consistency ratio is calculated by whatever CR is closer to zero, the results have higher consistency.

Table 3

Consistency index (CI) based on You et al. (2017)

	(EI)	(WI)	(FI)	(VI)	(AI)
a~_BW	(1, 1, 1)	(0.667, 1, 1.5)	(1.5, 2, 2.5)	(2.5, 3, 3.5)	(3.5, 4, 4.5)
CI	3.00	3.80	5.29	6.69	8.04

FANP

ANP is one of the MADM methods that is general mode of the AHP developed by Saaty (1996). Unlike the AHP, the ANP can incorporate interrelationships between criteria/sub-criteria among the decision levels. This method applies ratio scale measurements according to pair wise comparisons. In the ANP-based systems, a level may both dominate and be dominated, indirectly or directly, by other levels. In general, the AHP is hierarchy-based and the ANP is network-based. The difference between a network and a hierarchy is illustrated in Fig. 2. In ANP method, the interrelationships between elements is handled by development of a “supermatrix” (Büyüközkan and Çifçi 2012). Component or cluster is shown using a node with elements inside it and an arc shows the interrelationships among two components. Since human judgment with exact numerical values is hard and preferences of decision makers are usually unclear, researchers extended ANP method to fuzzy ANP which is adapted with fuzzy environment.

Fig. 2

Structure of a network and a hierarchy

FIS

FIS is a rule-based system that estimates an output based on rules made by decision makers. FIS is considered as an expert system. This approach works based on the rules made by the experts. Unlike other decision-making methods, FIS does not need the historical data set. That is, this system works based on the rules. This system contains membership functions, logic operators, and IF-THEN rules. These rules are applied to mimic the human reasoning process. There are two types of FIS known as Mamdani and Sugeno (Ilbahar et al. 2018). Mamdani-based FIS is the most widely used FIS for approximating an output using IF-THEN rules. In a Mamdani-based structure, inputs are applied as: IF x1 (first input) is O1 (first linguistic variable) AND x2 (second input) is O2 (second linguistic variable) AND xn (nth input) is On (nth linguistic variable) THEN y is D (the output). The inputs can be fuzzy or exact numbers. For more information, please refer to Amindoust et al. (2012).

In FIS, the fuzzy rules are normally generated based on experts’ opinions. Experts can make as many rules as they want. However, if there are C criteria and M membership functions, the number of rules needed is MC. For example, if there are 12 criteria and 5 membership functions, the number of rules will be 244140625. In order to avoid an exhaustive number of rules, experts can make the rules based on only two inputs at a time (Amindoust et al. 2012) (if C = 2 and M = 5, the number of rules is 25). It means that the number of rules follows the number of the membership function. If the number of membership function decreases, the number of rules decrease, and if the number of function increases, the number of rules increases. For instance, if the number of the membership function is 2, the number of rules is 22 = 4 or if the number of the membership function is 7, the number of rules is 27 = 128. In this research, a meeting with the experts of the case company was conducted to discuss the way of making the rules for performance evaluation. As a result, the fuzzy rule base as shown in Table 4 was developed and the following five initial membership functions were used:

Table 4

The fuzzy rule base

Second input	First input
	VP	P	M	G	VG
VP	VP	VP	P	P	M
P	VP	P	P	M	M
M	P	P	M	M	G
G	P	M	M	G	G
VG	M	M	G	G	VG

Very poor (VP) = (1,2,3)

Poor (P) = (2,3,4)

Moderate (M) = (3,4,5)

Good (G) = (4,5,6)

Very good (VG) = (5,6,7)

The fuzzy input numbers are defuzzified into exact or crisp values using Equation (4) (the GMIR method). The crisp values are then employed as inputs to the FIS. In order to execute the FIS, two inputs are used at a time for obtaining one output based on the reason explained earlier. In the process of selecting two-by-two inputs, any remainder which is not chosen will be treated as an input for the next hierarchical level (Amindoust et al. 2012). This process is continued until all the inputs are used in the FIS.

Aggregation method

Assume that is the aggregated TFN of the importance degree of ith criterion where a number of experts are involved in the evaluation process, the aggregated importance degree of each criterion is computed as

where d is the number of experts and denotes the kth expert’s thought for the importance degree of ith criterion. Suppose is the aggregated TFN of the performance rating of a supplier based on ith criterion. The aggregated value is calculated as

where d is the number of experts and represents the kth expert’s thought for the performance rating of a supplier based on ith criterion.

The developed hyper-hybrid model

In this, the proposed model is explained step by step (see Fig. 3). The first phase of the model is to determine the most suitable resilient-sustainable criteria (localization). To this end, first a comprehensive list of criteria is presented (based on the literature and experts’ opinions). Then, the importance and applicability of each criterion are measured. Finally, those criteria which are both important and applicable are selected as the evaluative attribute. In fact, this paper applies the criteria that are really suitable in real-world problem. To measure the importance and applicability of the model, we use statistical test. After determining the initial list of criteria, several questionnaires are developed and distributed to the experts. Then, the experts are asked to measure their importance and applicability. If the distribution of the data set is normal, parametric statistical test is applied, and if the distribution of the data set (collected from the questionnaires) is not normal, non-parametric statistical test is applied. Finally, based on the statistical results, the most appropriate criteria (the most important and applicable criteria) are selected. As it is seen in the second phase of the model, the first step of this phase is to gather data set for determining the interrelation between the criteria using FDEMATEL. Moreover, in this step, the best and the worst criteria are specified. In the second step of the model, the initial (local) weights of the criteria and their corresponding sub-criteria are calculated employing the FBWM. In the last step of this phase, the final weight of each sub-criterion is computed based on the determined interrelations (using FDEMATEL) between the criteria by applying the FANP. In this regard, at first, without considering the interrelationships, the initial weights are calculated by the fuzzy BWM using LINGO software (to reduce the cognitive burden and to increase the reliability of the results). Afterwards, we apply fuzzy ANP to calculate the final weights of the aspects/criteria in which the interrelationships are considered employing Superdecision software.

Fig. 3

The phases of the proposed hyper-hybrid decision-making framework

After obtaining the final weights, the FIS system is implemented. The first step of the third phase of the developed model is collecting data set based on the proposed five linguistic terms (VP to VG). Then, the crisp values are calculated using GMIR. Certainly, these values are between 1 and 7 (as the range of the linguistic terms is between 1 and 7). These values are then multiplied with the importance weights. Since the importance weights are between 0 and 1, the range of the weighted data set is reduced, and consequently, all the numbers can fall into the very poor (VP) category, thus rendering the suppliers’ performance as weak. In order to solve this problem, the weighted data set is normalized using Equation (10).

where NWD is the normalized weighted data for a criterion of a supplier, WD is the weighted data for a criterion of a supplier, and MPWD is the maximum possible weighted data for a criterion of a supplier. The computed NWD values will be in the range from 0 to 100, but the range of the initial linguistic terms or membership functions used by the experts is between 1 and 7. In order to address this problem, in the second stage, new membership functions between 0 and 100 are defined as follows:

Having obtained the NWD values and using the second stage membership functions, the two-by-two FIS is run for each supplier based on all the resilient-based sustainability criteria and the performance of each supplier is computed.

Case study and computational results

This section includes two sub-sections. In the first subsection, the case company is presented. Then, in the second sub-section, the obtained results from the proposed hyper-hybrid fuzzy framework are presented.

Case company

As it is seen in Fig. 4, there are three main regions in Malaysia for palm oil plantation including Johor, Pahang, and Perak. Therefore, there are many palm oil manufacturing industries in these three states of Malaysia. Palm oil production is vital for the economy of Malaysia, which is the world’s second-largest producer of the commodity after Indonesia. Palm oil is one of the Malaysia’s primary industries. Malaysian companies also dominate the global palm oil industry. Palm oil is found in most consumer goods, from cosmetics to confectionery.

Fig. 4

Three main regions of Malaysia for palm oil plantation

To apply the developed hyper hybrid model, a real case company in palm oil industry has been selected in Johor, called “company ZAZA” hereafter. Company ZAZA provides various products such as Refined, Bleached and Deodorised (RBD) Palm Olein, RBD Palm Oil, RBD Palm Stearin, Red Palm Oil, RBD Palm Kernel Oil and so on. In the last decades, it is known as one of the top five palm oil-manufacturing industries in Malaysia. To remain competitive in the market, company ZAZA needs to have a strong partnership with its suppliers. In fact, the company motivates its six suppliers to regularly improve their manufacturing operations in order to procure sustainable materials from them. The company strongly believes that incorporating resiliency attributes into the field of sustainable supplier selection results in selecting the most capable suppliers for such partnership. Three experts from company ZAZA participated in the data collection process. The first expert is the warehouse manager with 8 years of experience in warehousing in the palm oil industry. The second expert is the procurement manager with 13 years of experience. The third one is the production manager with 23 years of experience in yarn production and spinning. These experts were asked to give their opinions about the importance degree of each criterion using the linguistic variables in Table 1. Moreover, they were asked to provide their opinions about the performance rating of each supplier based on each criterion using the initial membership functions defined in “Aggregation method”. In addition, it should be mentioned that according to Morgan table (Krejcie and Morgan 1970), 384 were selected as the experts for the questionnaire-based survey (measuring importance and applicability).

Evaluative RS criteria

As stated before (the first phase of Fig. 3), the first aim of this study is to provide a list of most important and applicable RS evaluative attributes for assessing suppliers.

Providing the initial list of RS criteria

A comprehensive list of the criteria for each of the aspects is collected based on the previous studies (such as Amindoust 2018; Fallahpour et al. 2017) and thoughts of the panel of the current research. In this paper, a list with three aspects (general, sustainability and resilient) including 30 criteria was provided. Definition of each criterion is presented in Table 5.

Table 5

Definition of the related sub-criteria

Aspect	Criterion	Definition
General	Quality-C1	This feature means the ability of provided goods to meets the customer’s expectations.
	Cost-C2	This feature shows the final cost which has been determined by the supplier.
	Delivery-C3	This feature means the ability of supplier in delivering of required goods to the customers.
	Flexibility-C4	The feature means the flexibility degree of supplier in providing goods, cost of the needed material, etc. for the customers.
	Service-C5	This feature means the ability of supplier in being responsible for the sold materials.
	Turnover-C6	This feature means the amount of money taken by the supplier in a particular period.
Sustainable	Resource consumption-C7	The feature means the ability of supplier in managing the use of energy and resources during providing the ordered materials.
	Eco-labeling-C8	This feature shows the level of responsibility of the supplier in using eco-labels for the requested goods.
	Pollution control-C9	This feature means the ability of the supplier in monitoring and controlling quantity of dangerous materials applied in generating the needed materials.
	Green certification-C10	This feature means the ability of the supplier in collecting green related certification in generating the needed materials.
	Re-use-C11	This feature means the effort of supplier in re-applying the generated goods.
	Air emissions-C12	This feature means the ability of the supplier in controlling quantity of dangerous emission such as HCL, NH3, SO2, and so on in generating the needed materials.
	Waste water-C13	This feature means the ability of supplier in controlling the use of waste water.
	Hazardous wastes-C14	This feature means the ability of supplier in minimizing the hazardous wastes.
	Workers’ contract-C15	This feature shows the level of responsibility of supplier for having contract with the workers.
	Employment insurance-C16	This feature shows the level of responsibility of supplier for having contract with the workers.
	Standard working hours-C17	This feature shows the level of responsibility of supplier for having standard working hours for the workers.
	Overtime pay-C18	This feature shows the level of responsibility of supplier for having over pay for the extra time working to the workers.
	Providing appropriate equipment at work-C19
	Growth at work- C20	This feature means the level of responsibility of supplier for improve the position of the workers at work according their experience.
	Considering the religious issues at work-C21	As Malaysia is a multi-national country (Indian, Malaysia, and Chines), the supplier must pay attention to the religions of the workers at works.
	Wages-C22	This feature means the level of responsibility of supplier for paying salary to the workers based on work law.
Resilient	Robustness-C23	This feature means the ability to withstand disruptions to elements within the supply network, either through the immediate availability of alternative suppliers or being capable of quickly planning the incorporation of new suppliers.
	Responsiveness-C24	This feature shows the ability of supplier in being responsiveness in different situations
	Cooperation-C25	This feature shows the ability of supplier in having cooperation with other suppliers and customers for improving the quality of materials.
	Agility-C26	This feature shows the ability of supplier in produce a product quickly.
	Visibility-C27	This feature shows the ability to share the related data, which would help the customers in using the product.
	Risk reduction-C28	This feature means the ability of supplier for predicting the different conditions and reducing the risk in difficult conditions.
	Surplus inventory-C29	Additional available inventory for crises or emergency
	Restorative capacity-C30	This feature shows the ability of supplier in restoring the low quality products for the customers.

Determining the most suitable criteria (localization-measuring importance and applicability)

In this step, a questionnaire is provided to measure how much the RS attributes are important and applicable for the Malaysian palm oil-manufacturing industry. The questionnaire has different parts. The first, second and third parts consist of the general, sustainability and resilient factors, respectively. In order to measure the importance and applicability, a 1 to 5 scale was applied to show that how much a criterion is important and applicable in a real problem. Please note that where 1 = very poor, 2 = poor, 3 =moderate, 4 = good and 5 = very good.

The questionnaire was sent to 384 experts (200 from academia and 184 from industry) in Malaysia to express their opinions about the importance and applicability of the collected list of RS criteria. All the completed questionnaires were collected within 40 days after distribution. The number of the completed questionnaires were 193 (50.26%). Seventy-eight from academia ( and 115 (59.38) from industry. Fallahpour et al. (2017) report that the value of 193 (50.26) is acceptable. The findings show that three criteria out of 33 criteria should be removed from the list (as there is difference between their importance and applicability) called technology, using green fuel, and discrimination. Table 6 shows the average values of importance and applicability of each attribute.

Table 6

The importance and applicability of the RS attributes

Criteria	Importance	Applicability
C1	4.315	4.072
C2	4.157	3.00
C3	4.152	4.715
C4	4.964	4.000
C5	4. 789	5.000
C6	3.356	3.354
C7	3.065	4.073
C8	5.000	4.000
C9	4.854	4.354
C10	4.064	4.718
C11	4.136	4.715
C12	4.064	3. 928
C13	4.178	4.000
C14	4.009	5.000
C15	4.741	4.963
C16	3.359	4.092
C17	4.000	4.381
C18	3.13157928	5.000
C19	4.774	3.000
C20	3.065	4.073
C21	3.891	3.899
C22	4.082	4.927
C23	4.811	3.350
C24	3.928	3.715
C25	5.000	4.356
C26	4.901	4.358
C27	4.070	4.009
C28	3.797	4.001
C29	5.000	4.964
C30	4.308	4.002

It should be mentioned that after collecting the questionnaire-based information, the reliability test was done to check that the instrument and information were reliable for further examination. Olugu et al., 2011stated that Cronbach’s alpha can examine the internal reliability of attributes. Both importance and applicability have 30 criteria for general, sustainable and resilient aspects. It should be informed that in this test, the alpha value should be greater than 0.7. The results are presented in Table 7.

Table 7

Importance and applicability of the determined RS criteria

Criteria	Importance	Applicability
C1	0.863	0.8144
C2	0.8314	0.761
C3	0.8304	0.943
C4	0.9928	0.800
C5	0.9578	0.897
C6	0.671	0.670
C7	0.613	0.814
C8	0.749	0.800
C9	0.970	0.870
C10	0.8128	0.9436
C11	0.8272	0.943
C12	0.8128	0.7856
C13	0.8356	0.800
C14	0.8018	0.972
C15	0.9482	0.9926
C16	0.6718	0.8184
C17	0.8	0.709
C18	0.754	0.825
C19	0.809	0.7008
C20	0.818	0.8112
C21	0.7782	0.7798
C22	0.81654	0.9854
C23	0.9622	0.67
C24	0.7856	0.743
C25	0.811	0.8712
C26	0.9802	0.8716
C27	0.814	0.8018
C28	0.7594	0.8002
C29	0.833	0.9928
C30	0.8616	0.8004

As the distribution of the data set is not normal, the second test was Mann–Whitney U test that show that the average values of data related to importance and applicability differ significantly. All the 30 criteria were evaluated by applying Mann–Whitney U test, and for all the attributes, the p value was bigger than 0.05 which means there is no big difference between importance and applicability of the listed criteria.

Computing the weighs of the criteria

In this section, the final weight of each criterion is calculated by integrating FDEMATEL, FBWM and FANP.

FDEMATEL results

This section is dedicated to present the achieved results from FDEMATEL method. This section is divided into four sections: (i) implementation of the FDEMATEL for criteria, (ii) implementation of the FDEMATEL for general sub-criteria, (iii) implementation of the FDEMATEL for sustainable sub-criteria and (iv) implementation of the FDEMATEL for resilience sub-criteria. It should be noted that to identify the interrelationships between the criteria/sub-criteria, the questionnaires are distributed between three groups of experts.

Criteria

Table 8 shows the average of opinions of three teams of experts for criteria and Fig. 5 illustrates the causal diagram of criteria. According to the results, resilience and sustainable criteria affect the general criteria. It should be noted that the details of the calculation process are given in Supplementary materials.

Table 8

The average of opinions of three teams of experts

	General			Sustainable			Resilient
	L	m	u	l	M	u	l	m	u
General	0.00	0.00	0.00	2.67	3.67	4.67	4.00	5.00	6.00
Sustainable	4.67	5.67	6.67	0.00	0.00	0.00	2.00	3.00	4.00
Resilient	4.67	5.67	6.67	2.67	3.67	4.67	0.00	0.00	0.00

Fig. 5

The causal diagram of criteria

On the other hand, as aforementioned, in this study, we apply the FDEMATEL method to determine the best and the worst criteria for the FBWM method. To do this, we consider criteria with higher D+R as the best and the criteria with the lowest D+R as the worst. It is necessary to mention, if for some criteria D+R is same, the best/worst criteria would be selected using expert opinion. Table 9 presents the values of the D+R for each criteria.

Table 9

Determining the best and the worst criteria

	General	Sustainable	Resilient	The best	The worst
D+R	17.57246026	15.33087817	16.27760184	General	Sustainable

General sub-criteria

In this section, the FDEMATEL method is applied to identify interrelationships among general sub-criteria. Figure 6 depicts the causal diagram of general sub-criteria. The detailed calculations are given in supplementary materials. The results show that quality, flexibility, delivery, service and turnover have effect on the cost criteria and also turnover affect the delivery.

Fig. 6

The causal diagram of general sub-criteria

The best and the worst general sub-criteria based on D+R are given in Table 10.

Table 10

Determining the best and the worst general sub-criteria

	Quality	Cost	Delivery	Flexibility	Service	Turnover	The best	The worst
D+R	2.118	4.171	2.449	1.821256215	1.8213	2.493	Cost	Flexibility

Sustainable sub-criteria

This section is devoted to identify the interrelationships among the sustainable sub-criteria applying FDEMATEL method. Table 11 shows the interrelationships between the sustainable sub-criteria. In this table, “aij = 1” means that the sub-criteria i has considerable effect on the sub-criteria j. Detailed calculations are given in Supplementary materials. The sub-criteria that are not mentioned in columns of Table 11 have no effect on any sub-criteria. Also, the best and the worst criteria are determined in Table 12.

Table 11

Interrelationships between sustainable sub-criteria

	Resource consumption	Eco-labeling	Pollution control	Workers’ contract
Resource consumption	0	1	0	0
Eco-labeling	1	0	0	0
Pollution control	1	1	0	0
Green certification	1	1	1	0
Re-use	1	1	1	0
Air emissions	1	1	1	0
Waste water	1	1	1	0
Hazardous wastes	1	1	1	0
Workers’ contract	0	0	0	0
Employment insurance	0	0	0	1
Standard working hours	0	0	1	1
Overtime pay	0	0	0	1
Considering the religious issues at work	0	0	0	0
Providing appropriate equipment at work	0	0	0	0
Growth at work	0	0	0	0
Wages	0	0	0	1

Table 12

Determining the best and the worst sustainable sub-criteria

	D+R	The best	The worst
Resource consumption	5.50116208	Resource consumption	Employment insurance
Eco-labeling	4.946729598
Pollution control	3.916078948
Green certification	3.004371652
Re-use	3.033204003
Air emissions	3.402841388
Waste water	3.355541397
Hazardous wastes	2.84325136
Workers’ contract	3.502177198
Employment insurance	1.145547192
Standard working hours	3.221520854
Overtime pay	2.496795215
Considering the religious issues at work	2.161667887
Providing appropriate equipment at work	2.170644512
Growth at work	2.161667887
Wages	2.488

Resilient sub-criteria

In this section, the results of FDEMATEL for resilient sub-criteria are presented. The interrelationships between these criteria are given in Table 13. On the other hand, the best and the worst criteria are determined in Table 14.

Table 13

Interrelationships between resilient sub-criteria

	Robustness	Responsiveness	Cooperation	Agility	Visibility	Risk reduction	Surplus inventory	Restorative capacity
Robustness	0	1	0	1	0	0	0	0
Responsiveness	0	0	0	1	0	0	0	0
Cooperation	1	1	0	1	0	1	0	0
Agility	0	1	0	0	0	0	0	0
Visibility	1	1	0	1	0	1	0	0
Risk reduction	1	1	0	1	0	0	0	0
Surplus inventory	1	1	0	1	0	0	0	0
Restorative capacity	1	1	0	1	0	0	0	0

Table 14

Determining the best and the worst resilient sub-criteria

	Robustness	Responsiveness	Cooperation	Agility	Visibility	Risk reduction	Surplus inventory	Restorative capacity	The best	The worst
D+R	4.4415	6.0404	3.2623	6.2646	3.0699	3.2118	3.3021	3.3036	Agility	Visibility

FBWM results (initial weights)

After identifying the interrelationships among criteria/sub-criteria and determining the best and the worst ones by applying the FDEMATEL method, in this section, the initial weights of criteria/sub-criteria are calculated using FBWM. To do this, the questionnaires are distributed between experts (the average of experts’ opinions are presented in Supplementary materials); afterwards, the corresponding models are solved and the results are obtained. Tables 15, 16, 17 and 18 show the achieved results from the FBWM.

Table 15

The results of FBWM for the criteria

Criteria	General	Sustainable	Resilient
Optimal weights	0.4356072	0.2445288	0.3198640
ξ∗= 0.2001220 CI=3.80 ➔ CR=0.20012203.80=0.052663

Table 16

The results of FBWM for the general sub-criteria

Sub-criteria	Quality	Cost	Delivery	Flexibility	Service	Turnover
Optimal weights	0.1964320	0.2978326	0.1715629	0.0844794	0.1243212	0.1253719
ξ∗= 0.68045 CI=8.04 ➔ CR=0.680458.04=0.08463

Table 17

The results of FBWM for the sustainable sub-criteria

Sub-criteria	Optimal weights	CR
Resource consumption	0.09964101	ξ∗= 0.8017642 CI=8.04 ➔ CR=0.80176428.04=0.09972
Eco-labeling	0.07478959
Pollution control	0.06330424
Green certification	0.05969768
Re-use	0.04659672
Air emissions	0.06057043
Waste water	0.06213666
Hazardous wastes	0.06215585
Workers’ contract	0.07151719
Employment insurance	0.02826119
Standard working hours	0.06232593
Overtime pay	0.06232201
Considering the religious issues at work	0.06232201
Providing appropriate equipment at work	0.06232201
Growth at work	0.06233981
Wages	0.05969768

Table 18

The results of FBWM for the resilient sub-criteria

Sub-criteria	Robustness	Responsiveness	Cooperation	Agility	Visibility	Risk reduction	Surplus inventory	Restorative capacity
Optimal weights	0.1027	0.2015	0.1014	0.2130	0.0529	0.1226	0.1027	0.1032
ξ∗= 0.7868032 CI=8.04 ➔ CR=0.78680328.04=0.0976

FANP results (final weights)

In the previous stages, we identify the interrelationships between criteria/sub-criteria and also calculate the initial weights of the criteria/sub-criteria using FBWM approach. Here, we obtain the final weights of the sub-criteria due to interrelationships between these elements by employing the FANP method. In this research, we apply the SuperDecisions software to obtain the final weights of the criteria and sub-criteria (the decision tree of the current problem in the mentioned software is depicted in Supplementary materials). The SuperDecisions is the free educational software that implements AHP and ANP. One of the important options of this software is the ability to enter the weights of elements, directly. In this paper, we used this option and the obtained weights from FBWM are directly entered to the SuperDecisions software utilizing “Misc ➔ Direct data entry” toolbar in pairwise comparison section that let us to enter the weight of elements Also, Table 19 shows the obtained results from FANP (final weights of the sub-criteria). Based on this table, cost and employment insurance are the most important and the least significant sub-criteria, respectively.

Table 19

The obtained results from FANP

Sub-criteria	Final weight
C1	0.128149
C2	0.194840
C3	0.194185
C4	0.054921
C5	0.081074
C6	0.081728
C7	0.019406
C8	0.008321
C9	0.007043
C10	0.006642
C11	0.005184
C12	0.006739
C13	0.006913
C14	0.006915
C15	0.007957
C16	0.003144
C17	0.006934
C18	0.006934
C19	0.006934
C20	0.006936
C21	0.006934
C22	0.006642
C23	0.013938
C24	0.027353
C25	0.013768
C26	0.028914
C27	0.016968
C28	0.016647
C29	0.013938
C30	0.014004

Ranking the suppliers using the developed two-by-two FIS model

As explained before, there are five steps in the developed tow-by-two FIS. Firstly, the performance ratings of six suppliers of company ZAZA with respect to each criterion were collected from the three experts based on the initial membership functions. The aggregated crisp values were multiplied with the global weights, respectively, to obtain the WD values. Then, the NWD values were computed by normalizing the WD values. Table 20 shows the aggregated crisp values, WD and NWD. After this step, the range of the initial membership functions was changed to between 0 and 100 as explained earlier. In this step, the NWD values were considered as the inputs. Based on two-by-two inputs, the FIS was executed to obtain the final performance value of each supplier. This weighted two-by-two FIS was run in MATLAB 2018b.

Table 20

WD and NWD of the suppliers with respect to the RS criteria

	C1	C2	C3	C4	C5	C6	C7	C8	C9	C10	C11	C12	C13	C14	C15	C16	C17	C18	C19	C20	C21	C22	C23	C24	C25	C26	C27	C28	C29	C30
S1	4.500	4.750	3.500	5.000	2.750	5.750	5.000	4.500	3.500	3.000	5.750	5.000	2.500	2.500	2.500	3.500	5.500	3.000	5.000	4.500	3.500	3.000	5.750	5.000	2.500	2.500	2.500	3.500	5.500	3.000
WD	0.135	0.033	0.049	0.975	0.534	0.040	0.040	0.014	0.067	0.165	0.040	0.035	0.018	0.018	0.018	0.448	0.028	0.081	0.070	0.077	0.049	0.243	0.040	0.070	0.205	0.043	0.018	0.025	0.039	0.024
NWD	64.286	67.857	50.000	71.429	39.286	82.143	71.429	64.286	50.000	42.85	82.143	71.429	35.714	35.714	35.714	50.337	78.571	42.857	71.429	64.286	50.000	42.857	82.143	71.429	418.367	86.735	35.714	50.000	78.571	48.980
S2	3.000	5.750	5.000	2.500	2.500	2.500	3.500	5.500	4.500	4.750	3.500	5.000	2.750	5.750	5.000	4.500	3.000	5.750	5.000	2.500	2.500	2.500	3.500	5.500	3.000	5.000	2.750	5.750	5.000	4.500
WD	0.090	0.040	0.070	0.488	0.485	0.018	0.028	0.017	0.086	0.261	0.025	0.035	0.019	0.040	0.035	0.576	0.015	0.155	0.070	0.043	0.035	0.203	0.025	0.077	0.246	0.085	0.019	0.040	0.035	0.036
NWD	42.857	82.143	71.429	35.714	35.714	35.714	50.000	78.571	64.286	67.857	50.000	71.429	39.286	82.143	71.429	64.286	42.857	82.143	71.429	43.367	35.714	413.265	50.000	78.571	42.857	71.429	39.286	82.143	71.429	64.286
S3	2.500	2.500	2.500	3.500	5.500	3.000	5.000	2.500	3.500	5.500	4.500	4.750	3.500	5.000	2.750	5.750	3.000	2.500	2.500	2.500	3.500	5.500	4.500	4.750	3.500	4.500	2.500	2.500	2.500	3.500
WD	0.075	0.018	0.035	0.683	1.067	0.021	0.040	0.008	0.067	0.303	0.032	0.033	0.025	0.035	0.019	0.736	0.015	0.068	0.035	0.043	0.049	0.446	0.032	0.067	0.287	0.077	0.018	0.018	0.018	0.028
NWD	35.714	35.714	35.714	50.000	78.571	42.857	71.429	35.714	50.000	78.571	64.286	67.857	50.000	71.429	39.286	82.143	42.857	35.714	35.714	43.367	50.000	909.184	64.286	67.857	50.000	64.286	35.714	35.714	35.714	50.000
S4	2.500	2.500	2.500	3.500	5.500	4.500	4.750	3.500	5.000	2.750	5.750	3.000	5.750	5.000	2.500	2.500	2.500	3.500	4.500	4.750	3.500	5.000	2.750	5.750	3.000	5.750	5.000	2.500	3.500	5.500
WD	0.075	0.018	0.035	0.683	1.067	0.032	0.038	0.011	0.095	0.151	0.040	0.021	0.040	0.035	0.018	0.320	0.013	0.095	0.063	0.081	0.049	0.405	0.019	0.081	0.246	0.098	0.035	0.018	0.025	0.044
NWD	35.714	35.714	35.714	50.000	78.571	64.286	67.857	50.000	71.429	39.286	82.143	42.857	82.143	71.429	35.714	35.714	35.714	50.000	64.286	82.398	50.000	826.531	39.286	82.143	42.857	82.143	71.429	35.714	50.000	78.571
S5	4.750	3.500	5.000	2.750	5.750	5.000	4.500	3.000	2.500	2.500	2.500	3.500	5.500	4.500	4.750	3.500	4.500	4.750	3.500	5.000	2.750	5.750	5.000	4.500	5.750	5.000	2.500	2.500	2.500	3.500
WD	0.143	0.025	0.070	0.536	1.116	0.035	0.036	0.009	0.048	0.138	0.018	0.025	0.039	0.032	0.033	0.448	0.023	0.128	0.049	0.085	0.039	0.466	0.035	0.063	0.472	0.085	0.018	0.018	0.018	0.028
NWD	67.857	50.000	71.429	39.286	82.143	71.429	64.286	42.857	35.714	35.714	35.714	50.000	78.571	64.286	67.857	50.000	64.286	67.857	50.000	86.735	39.286	950.510	71.429	64.286	82.143	71.429	35.714	35.714	35.714	50.000
S6	3.000	4.750	5.000	2.500	2.500	2.500	3.500	5.500	4.500	4.750	3.500	5.000	2.750	5.750	5.000	4.500	3.000	5.750	5.000	2.500	2.500	2.500	3.500	5.500	3.000	5.000	2.750	5.750	5.000	4.500
WD	0.090	0.040	0.070	0.488	0.485	0.018	0.028	0.017	0.086	0.261	0.025	0.035	0.019	0.040	0.035	0.576	0.015	0.155	0.070	0.043	0.035	0.203	0.025	0.077	0.246	0.085	0.019	0.040	0.035	0.036
NWD	42.857	82.143	71.429	35.714	35.714	35.714	50.000	78.571	64.286	67.857	50.000	71.429	39.286	82.143	71.429	64.286	42.857	82.143	71.429	43.367	35.714	413.265	50.000	78.571	42.857	71.429	39.286	82.143	71.429	64.286

The application of FIS can be shown by a surface. For example, the surface of the FIS operation associated with C1 and C2 for supplier 1 (S1) is depicted in Fig. 7. In this figure, the output is shown based on C1 and C2. It can be observed that, when C1 and C2 have low amounts, the performance (output) has small value. It means that C1 and C2 directly influence on the performance. Moreover, when the numbers of C1 and C2 increase, the output value increases. After completing all the FIS operations, the performance value of a supplier was computed. This process was applied for each supplier, and among the six suppliers, S5 (performance = 6.357) is the best, followed by S4 (performance = 6.119), S3 (performance = 5.978), S1 (performance = 5.577), S6 (performance = 5.228) and S2 (performance = 3.748).

Fig. 7

Surface of the FIS operation related to criteria C1 and C2 for the first supplier

Validation of the proposed model

There are different techniques for verifying the validity of decision-making models. In this study, in order to validate the robustness of the model, the following two approaches were used: (i) checking the consistency ratio (CR) for FBWM (Guo and Zhao 2017), (ii) using different defuzzification methods such as center of area (COA), bisector of area (BOA), mean of maximum (MOM), smallest of maximum (SOM) and largest of maximum (LOM) for FIS (Amindoust et al. 2012; Amindoust and Saghafinia 2017).

Checking the CR

Guo and Zhao (2017) mentioned that CR must be close to zero to reflect a high consistency. The CR value for the aspect comparison is 0.059. With regard to the economic criteria comparison, the CR value is 0.038. In terms of the environmental and social criteria comparisons, the CR values are 0.040 and 0.059, respectively. As these numbers are close to zero, it can be concluded that all the comparisons are consistent. Hence, the global weights are reliable and the model is applicable.

Using different defuzzification methods

Sensitivity analysis via changing the defuzzification method helps to evaluate the robustness of a FIS-based model. In this respect, five different methods (COA, BOA, MOM, SOM and LOM) were analyzed. Table 21 shows that by changing the defuzzification method, the rankings of the suppliers are relatively similar and S3 is still the best supplier based on the RS criteria. This indicates that the model is robust and valid.

Table 21

Ranking of the suppliers

	COA	BOA	MOM	SOM	LOM
S5	6.357	6.947	6.889	6.997	6.116
S4	6.119	6.852	6.703	6.443	5.947
S3	5.978	6.009	5.297	6.128	5.736
S1	5.577	5.753	5.014	5.823	5.654
S6	5.228	5.213	4.302	5.005	5.302
S2	3.748	4.007	3.792	4.456	3.231

Findings and discussion

Prioritizing the best suppliers based on the multiple criteria is a complex process (Fallahpour et al. 2017), specifically when gathering precise data is difficult. Proposing a decision-making model with fuzzy numbers aids the decision makers to show this issue. In the current paper, a novel combined model including FDEMATEL-FBWM-FANP and two-by-two FIS was proposed for supplier selection using RS criteria. Moreover, this is the first time that the importance and applicability of the resilient-based sustainable criteria were measured for assessing suppliers’ performance in palm oil industry. Figure 3 shows that there are three phases in this model which are determining the most important and applicable criteria, weighting the criteria by hybridizing FDEMATEL-FBWM-FANP and running the two-by-two FIS. A palm oil company was applied as a case study to show the model, where the questionnaires were distributed among three decision makers (managers) for gathering the data set to measure the performance and prioritize the suppliers.

In the first phase of the research, 30 localized RS criteria were determined for assessing suppliers’ performance in palm oil industry of Malaysia. To this end, questionnaires were developed and distributed to the experts for determining the importance and applicability of the listed criteria in Malaysian palm oil industry. After collecting the questionnaires and after doing the related statistical tests, it was shown that all the selected criteria are important for use in this study.

The weighting computation reveals that the economic (general) dimension is the most important aspect in resilient-based sustainable supplier selection. This is in line with the results of previous studies in the sustainable supplier selection area. The obtained results from FDEMATEL illustrated that the “sustainable” and “resilience” criteria have effect on the “general” criteria. Also, the interrelationships between the sub-criteria are shown using FDEMATEL. It is shown that ‘Price’ is the most crucial economic criterion, while ‘Resource consumption’ is the most important sustainable criterion and ‘Agility’ is the most important resilient attribute. The results indicate that the managers of the case company emphasize more on ‘Delivery than Quality’ (as the global weight for flexibility is 0.1942 and that for quality is 0.01281). Moreover, ‘Service’ is another crucial attribute based on the managers’ opinions. Criteria such as standard working hours, overtime pay, providing appropriate equipment at work and growth at work have the similar importance degree based on the managers’ opinions. In addition, turnover is the least important criterion for evaluating suppliers.

After implementing the two-by-two FIS, the results specify that S5 is the most appropriate supplier, followed by S4 and S3. The weakest supplier is S2. Moreover, two different techniques were used to prove the strength and validity of the proposed decision-making framework. The first technique was checking the CR values. The findings show that the CR numbers for all the comparisons are close to zero, which indicate that the consistency of the calculations is good. The second method was applying different defuzzification methods.

Managerial implications

The implications of this research include two parts: (i) combination of resilient criteria with sustainability criteria for sustainable supplier selection and (ii) development of a hyper hybrid FDEMATEL-FBWMFANP-two-by-two FIS model. This study has created a practical list of resilient-based sustainability attributes for suppliers’ performance assessment. Specifically, 30 most important and applicable criteria were provided based on three aspects (general, sustainability and resilient). The definition of each attribute is helpful for managers to have better understanding about the concepts of resiliency and sustainability for supplier selection. The final weights gained for the attributes can also be used as a pointer for managers to establish their preferences in resilient-based sustainable supplier selection. Moreover, an influential hybridized model has been developed to assess suppliers with respect to the selected attributes. By applying this model, managers can identify and select suppliers which are resilient-capable and economically and sustainability appropriate. In addition, the provided list of the attribute can be very applicable for the managers of the palm oil industry in Malaysia. Managers can understand the concept of resiliency as well as sustainability.

Theoretical implications

The concept of resiliency impresses the procedure of a sustainable supply chain. The current investigation has improved the literature by connecting resiliency to sustainable supply chain management. Especially, it has enriched the sustainable supplier selection context by taking into account resilient criteria together with sustainability factors. The list of RS attributes created from this paper can act as a realistic checklist for academics to explore the significant criteria for RS-based supplier selection. Practitioners can also apply the attributes to develop new models that will further expand the area. Moreover, FDEMATEL-FBWMFANP-two-by-two FIS has some advantages such as obtaining the interrelationships between criteria/sub-criteria by employing FDEMATEL, decreasing cognitive burden, increasing reliability of the results, and also considering interrelationships of the criteria in calculation of weights by integrating FBWM and FANP, and capability of measuring the suppliers’ performance one by one by applying FIS. It should be noted that the FIS model is absolutely new in the area of RS-based supplier selection. Unlike other models, the developed model does not calculate the performance relatively. In fact, this model provides the absolute performance value. It means that this model enables the managers to add new suppliers as many as they want. Moreover, the developed two-by-two FIS model is an open-ended model which means this model can be used for any number of criteria.

Conclusions, limitations and future work

There is a need to focus on resiliency in the concept of sustainable supply chain management. Especially, papers that have integrated resilient criteria with sustainability attributes for supplier selection are limited. Most of the developed assessment frameworks measure the relative performance of suppliers. There is no paper in which the importance and applicability of the resilient-based sustainable criteria for suppliers’ performance evaluation have been measured. Hence, this study aims at conducting a research that both provides a comprehensive list of the most important and applicable RS criteria and develops a hyper integrated FDEMATEL-FBWM-FANP-two-by-two FIS model for the first time to evaluate and select suppliers using resilient-based sustainability criteria. In essence, the integrated decision-making framework enables managers to evaluate suppliers individually and select the most appropriate supplier in an uncertain environment.

In fact, this research provides a comprehensive list of most important and applicable attributes for Malaysian palm oil industry as the localized attributes. That is, this list can be very applicable for the managers. Moreover, the definitions presented in this research help the Malaysian decision makers in this industry to have a better understanding about sustainability and resiliency. Also, this research shows the interrelationships between the criteria which means the managers recognize the interrelationships between the criteria. In addition, in this investigation, the importance degree of each criterion was shown. So, the managers of this industry can prioritize the evaluative criteria. Besides, a new two-by-two FIS model was developed which solves the problem of relative performance evaluation. Indeed, unlike other MCDM methods that need a complete decision matrix for performance evaluation, this model only needs the data set of the supplier under evaluation. Moreover, this model is able to handle the new data set for the new added supplier without having to re-run the performance evaluation for all the suppliers.

The developed model has only been applied in a palm oil company in Malaysia, and thus, the findings from this research cannot be generalized to other industries or countries. The evaluative criteria and their importance could be different for every industry or country. Hence, researchers can use different number and type of criteria for resilient-based sustainable supplier selection to suit the industrial and geographical contexts of their studies.

In the future, development of new models or integration of other methods can be done to spur more research in this area.

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