Research Opportunities for Supplier Selection: An Analysis from Literature Reviews

This article aims to identify different literature reviews of supplier selection to analyze the topics addressed in these documents, and suggest research opportunities for future literature reviews in issues that have not been addressed in the literature or require a deeper approach. This study states that the majority of existing literature reviews focus on the analysis of supplier selection methods and criteria, and uncertainty management, environmental management, and sustainability have been addressed in recent years. As a conclusion, it is suggested to focus future literature reviews on topics such as risk management, statistical methods, methods applied to industry sectors, implementation of supplier selection to small and medium enterprises, comparative analysis of solution methods performance, and the adaptation of solution methods from areas different to supplier selection. Likewise, it is recommended to continue updating literature reviews related to green and sustainable supplier selection, and uncertainty management in supplier selection, especially for the last 3-5 years.

demand of final consumers, improving the competitiveness and all material flows from raw materials to finished products (Amin-Tahmasbi & Alfi, 2018).
For a proper integration of the links in a supply chain, it is essential to perform efficient sourcing and purchasing processes (Aissaoui, Haouari, & Hassini, 2007), which are responsible for acquiring goods, components and services from suppliers, guaranteeing the viability of operations in a company through inflows and resource availability (Drake, Myung Lee, & Hussain, 2013). Therefore, the procurement and purchasing process represents a highly important role in most industries, to the point of representing between 70-80% of the total production cost, thus, a small reduction in purchasing costs can lead to a substantial increase in efficiency and profitability in companies (Ghodsypour & O'Brien, 2001;Murray, 2009).
Additionally, companies have increasingly been interested in reducing the number of suppliers to establish long-term relationships with reliable partners to improve the supply chain performance (Abdolshah, 2013;Kellner, Lienland, & Utz, 2018). Consequently, supplier selection is one of the most important and fundamental decisions in procurement and purchasing processes, drawing significant attention in the literature and practice due to the degree of difficulty involved in this multi-criteria decision-making process ( As supplier selection provides useful information to managers in supply chains and purchasing processes, it is necessary to review current studies in the literature in order to identify trends, research opportunities, criteria selection, uncertainty management, and supplier selection methods to support strategic plans in companies (Alkahtani & Kaid, 2018;Gómez, Cano & Campo, 2016 Accordingly, several literature reviews differ in their approach to supplier selection activities, the period analyzed, and the new studies and developments in these periods. For instance, Scopus provides 1,766 documents between 2000 and 2018 as a result of the search equation "supplier selection" in the field "article title", therefore, it is necessary to update existing literature reviews for supplier selection. Figure 1 shows the number of publications related to supplier selection and the growing trend of these publications in the last three years, where 30% of documents on supplier selection (525 publications) were published between 2016 and 2018, and 90% of documents were published between 2008 and 2018. Therefore, this article aims to identify the different literature reviews related to supplier selection to analyze the issues addressed therein and highlight research opportunities to conduct literature reviews based on previous studies or based on topics that have not yet been fully addressed in the scientific and academic field.

Literature reviews of supplier selection
As shown in Table 1, a wide variety of literature reviews of supplier selection has emerged since 2000, focusing on topics such as solution methods, analysis of the most recurrent and important criteria, uncertainty management for the decisionmaking process, application of supplier selection to industrial sectors, and other relevant issues.   Table 1 identifies that since 2001 the study of methods and criteria for supplier selection has prevailed as the central topic in literature reviews, and, later on, the uncertainty management, environmental management, and sustainability began to be relevant in literature reviews from 2013.
Analyzing the number of literature reviews per year, Figure 2 shows that this type of documents is growing over time, highlighting the importance of continuing analyzing new trends and research opportunities in topics related to supplier selection. Likewise, it is highlighted that the largest number of these documents was published in 2013 (five literature reviews), focusing on topics such as supplier selection methods, supplier selection criteria, uncertainty management, and environmental management.  Regarding the areas of knowledge, supplier selection documents stand out in the same areas as the literature reviews, mainly in the area of engineering, followed by the areas of computer science, business, management and accounting, decision science, and mathematics.  Due to the increasing number of publications in recent years regarding supplier selection (Figure 1), future literature reviews should consider short time periods, between 3 and 5 years, allowing analyzing new advances in specific themes of supplier selection, complementing existing literature reviews and avoiding the replication of information published and analyzed by other authors.

Conclusions
In this article, 28 literature reviews of supplier selection between 2000 and 2018 were analyzed, identifying that supplier selection is a multidisciplinary process involving areas such as engineering, business, management and accounting, computer science, decision science, and mathematics. Likewise, it is suggested to conduct literature reviews addressing risk management for supplier selection. Literature reviews of statistical methods in supplier selection are also encouraged, including techniques such as factor analysis, data mining, analysis of variance, multiple regression, decision trees, discriminant analysis, multivariate analysis of variance, sensitivity analysis, among others. These methods have been mentioned only by Alkahtani & Kaid (2018), but it is necessary to deepen in the utility and relevance of these methods for specific cases.
Another research opportunity is related to performing literature reviews focused on the application of supplier selection to real sectors, analyzing how methods and criteria are adjusted and selected according to the specific situation of each company. For example, future research could analyze which supplier selection models are used and how they differ from others for the Electric-Electronic sector, which represents the industry with the largest number of applications in the literature (Junior et al., 2013;Zimmer et al., 2016). Researchers interested in supplier selection are also encouraged to propose literature reviews of supplier selection methods and criteria for small and medium-sized companies, highlighting the differences with the approaches for large companies, and recommending computer environments to develop solution methods for companies with limited resources.
To the best of our knowledge, there are still no literature reviews of supplier selection allowing to compare the relevance and performance of supplier selection methods. This represents an opportunity to propose a guide to compare individual methods and hybrid methods, to the point of suggesting which combination of these methods are most effective under specific conditions of the supplier selection process. Additionally, it is recommended to review decisionmaking methods used in other areas of knowledge with similar conditions and objectives to those of the supplier selection, Likewise, it is suggested to continue presenting literature reviews of green and sustainable supplier selection, and also in topics related to uncertainty management, both through stochastic and fuzzy methods. Based on the growing trend of published documents, we recommend focusing future literature reviews in short time periods between 3 and 5 years, thus analyzing the contribution of new documents and avoiding the repetition of information provided by other authors.