Andrea et al. (2017) [1] undertakes a comprehensive evaluation of the public procurement literature by analyzing research published in the Journal of Public Procurement from 2001 to 2014. A total of 231 research outputs were systematically collected and examined, focusing on aspects such as the theoretical frameworks employed, research methodologies utilized, and the content of the papers. Through this analysis, the study offers an overview of previous research topics and findings while pinpointing key gaps in the existing literature. Manuel et al. (2019) [2] focuses on the situation of Spanish Public Procurement processes and available open data sources, particularly related to Request-For-Proposal (RFP) and tender submission data. It also covers relevant European and Spanish legislation and explains the Spanish Public Sector Contracting Platform, where procurement announcements and resolutions are published. It emphasizes how the analysis of public tenders can benefit various stakeholders, including politicians, public managers, project managers, executives, and citizens.

Then, what about sustainability? Monica et al. (2020) [3] aims to assess the level of sustainability integration into Canadian government procurement and offer recommendations to enhance the practices. Through a review of 50 publicly available Requests for Proposals (RFPs) issued from 2016 to 2019, the study evaluates the extent and depth of sustainability considerations and findings indicate that sustainability integration in RFPs is superficial, with limited inclusion in the evaluation process and narrow scope in environmental and social impact areas. Alok et al. (2020) [4] addresses the complex dynamics influencing sustainable public procurement, particularly in the context of developed and developing economies. Utilizing data collected from 546 public procurement practitioners across 102 countries, a structural equation model is developed and the conceptual model is validated across three categories of public procurement: goods, works, and services. Findings reveal that institutional pressures and citizens' attitudes towards sustainability significantly influence the level of sustainability adoption in public procurement. Moreover, the impact of these pressures varies between developed and developing economies.

What hinders sustainability? Javier et al. (2019) [5] aims to improve sustainable public procurement by identifying challenges faced by public servants and social economy entities. Surveys and interviews were conducted with 217 respondents from Spain and Europe. Findings were analyzed using a SWOT framework. The result shows that challenges include lack of training and internal resistance to change for the public sector, and small size and conflicts with social objectives for social entities. Adela et al. (2016) [6] investigates sustainable procurement practices in Saudi Arabian public and private organizations, aiming to understand their nature, extent, and the main barriers to implementation. Through a structured questionnaire survey involving 202 procurement directors/senior managers, the study employs multivariate and multiple regression techniques to analyze the relationship between organizations' sustainable procurement practices and barriers to implementation. Results indicate a predominantly negative state of sustainable procurement practices across organizations, with top management attitudes and organizational culture identified as primary barriers. Syed. et al. (2019) [7] aims to assess critical factors hindering the implementation of sustainable procurement in the public sector of Pakistan. Utilizing the Interpretive Structural Model, twelve key barriers to sustainable procurement implementation were identified and ranked based on literature review and Likert scale instrument. Analysis of tender documents from 75 public sector universities revealed a lack of sustainability elements. External factors such as government legislation and stakeholders' pressure were identified as the most critical barriers compared to inter-organizational factors. Based on a performance appraisal project conducted by the Guangzhou municipal government from 2012 to 2014, Li (2015) [8] identifies various challenges hindering the sustainable development of government procurement of public services. Using Guangzhou as a representative case study, the paper proposes several recommendations for ensuring the sustainable development of government procurement of public services, with a focus on addressing social work's resource dependence. Laura et al. (2019) [9] examines the impact of project-delivery methods and procurement procedures on the inclusion of social criteria in public construction procurement. Analyzing 451 tendering documents from 10 countries, content analysis, descriptive statistics, and logistic regression were applied. The findings highlight the influence of country and contract size on the inclusion of social criteria, with no significant differences observed between project-delivery methods or procurement procedures. However, certain social criteria were more prevalent in traditional delivery methods, while others were associated with lowest price procurement procedures. Laura et al. (2020) [10] addresses the barriers hindering the implementation of sustainability in public procurement within the construction industry. It highlights the lack of knowledge about which sustainability criteria to include and the subjectivity in defining their importance levels. To address this, the study aims to identify sustainability shortcomings in each European Union country and determine the importance of each sustainability category. Five environmental and eight social categories were established, and 42 national indicators were selected to assess sustainability performance across the 28 European countries using the Promethee method. Through cluster analysis, two groups of countries were identified: economically developed countries focusing on environmental performance, and others needing to balance social and environmental sustainability efforts. Helen & Stephen (2012) [11] investigates the interplay between sustainable procurement and e-procurement, two contemporary approaches in public procurement across numerous countries. Through a survey involving more than 280 public procurement professionals from 20 countries, responsible for a combined expenditure of $45 billion, the researchers explore the adoption of sustainable procurement and e-procurement. Utilizing multiple regression analysis, they construct a model illustrating that while e-procurement and effective communication with suppliers can facilitate certain aspects of sustainable procurement such as environmental, labor, and health and safety considerations, they may also impede other aspects. Specifically, e-procurement might hinder procurement from small local businesses that lack electronic capabilities.

Followed is regarding sustainability implementation. Mohamed & Charles (2016) [12] emphasizes the importance of considering the social dimension of sustainability in highway projects, alongside environmental and economic aspects. While many studies focus primarily on environmental sustainability, this study highlights the need to address social factors such as respect, awareness, diversity, vitality, and responsibility towards the workforce and society. The study identifies ten core factors crucial for social sustainability in highway projects and recommends their implementation at various stages of project development. Stephen & Helen (2010) [13] seeks to address gaps in understanding regarding sustainable procurement (SP) practices in public sector organizations internationally. The authors report findings from a survey of over 280 public procurement practitioners from 20 countries with a combined annual expenditure of $45 billion. Analysis reveals varying degrees of SP practices across regions, with some practices being evident in public procurement. The authors also identify key facilitators and barriers to SP engagement and investigate their significance for different dimensions of SP implementation. Azapagica & Perdan (2000) [14] addresses the pressing need for greater adoption of sustainable strategies in industry, focusing on the measurement of sustainability within industry, the paper proposes a comprehensive yet accessible framework comprising indicators across environmental, economic, and social dimensions. These indicators encompass factors such as environmental impacts, financial considerations, and ethical practices. While the framework is designed to be applicable across various industries, it emphasizes the importance of tailoring specific indicators to individual sectors. Lutz (2009) [15] aims to investigate how local government authorities in England utilize their procurement function to promote sustainable development, an area that has received less attention compared to the private sector. Employing an exploratory approach, the study involves qualitative research into leading local government authorities, building on existing literature. The findings reveal a variety of initiatives adopted by local government procurers to address all dimensions of sustainability. These initiatives are synthesized into a typology of sustainable supply chain management tailored for the public sector.

Stefan et al. (2012) [16] presents a rigorous examination of research in socially and environmentally responsible procurement (SERP), incorporating both quantitative and qualitative techniques. It underscores the critical juncture in SERP literature development and identifies shortcomings and potential fragmentation, emphasizing the importance of addressing these issues for SERP to become prominent in wider management discourse. The review provides a systematic analysis of existing contributions and their implications for practitioners, while also identifying neglected areas for future research critical from both academic and implementation perspectives. Joyce & Tim (2007) [17] examines the feasibility of implementing green procurement within English local government. Through desk research and interviews with five local authorities, it explores the background and current status of green procurement. The study reveals that while legislation, information provision, and barrier removal have encouraged green procurement, momentum was lost after the Gershon review. The analysis suggests that implementing a new action plan would embed green procurement within government practices. Additionally, linking green procurement with organizational goals could further expand its scope and impact. David et al. (2017) [18] presents a transparent and easily applicable methodology for selecting indicators of environmental sustainability, with the ultimate goal of enabling the comprehensive assessment of a country's environmental performance. The paper evaluates the utility of existing environmental sustainability indicators based on criteria such as policy relevance, utility, soundness, and data availability. By establishing differentiated indicator targets tailored to each nation's specific context, the methodology ensures that indicators are relevant to the unique circumstances of each country rather than applying generic regional standards. Francesco et al. (2016) [19] examines the factors influencing the inclusion of environmental criteria in public tenders, focusing on the context of Italian municipalities. The analysis indicates that increasing awareness and providing information about green public procurement (GPP) techniques significantly contribute to the development of environmentally friendly procurement practices. Additionally, the research highlights that the effectiveness of GPP is not solely dependent on the adoption of a certified Environmental Management System (EMS) by public authorities, but rather on the maturity level of the EMS, which adds value to GPP practices. Furthermore, the study suggests that despite limitations posed by the small size of public authorities, progress in GPP can be achieved through various European, national, and local support initiatives. Jolien & Dylan (2019) [20] investigates the impact of ability, motivation, and opportunity on six types of sustainable public procurement (SPP) policies: green procurement, social return on investment, circular economy, bio-based procurement, innovation-oriented procurement, and international social criteria. Through an online survey of procurers in Dutch public organizations, the study reveals that ability, motivation, and opportunity influence Green Public Procurement (GPP). Specifically, opportunity affects GPP, innovation-oriented procurement, and circular economy, but not other types of SPP. Bader et al. (2019) [21] explores internal factors influencing green procurement implementation in the United Arab Emirates (UAE) public sector, focusing on the relationship between organizational innovation capability and green procurement implementation, mediated by employees' commitment to change. A structural model is proposed using scales from literature, and primary research data collected from a cross-sectional survey of 50 respondents from public-sector organizations in Abu Dhabi. Findings indicate a positive influence of organizational innovation capability on green procurement implementation, alongside the impact of employees' commitment to change. Junqi et al. (2009) [22] investigates factors influencing the performance of Green Public Procurement (GPP) among Chinese procurement officials. Using data from 139 local government officials in China, a new conceptual model with direct and moderating effects was developed. The study reveals that officials' awareness of GPP implementation policies positively impacts their GPP performance. Additionally, receiving GPP training and working in local governments participating in the China national sustainable community (CNSC) program can positively moderate this relationship. However, awareness of GPP-related regulations does not have the same effect, and the mature CNSC program does not directly impact GPP performance. Francesco et al. (2016) [23] examines the incorporation of green criteria in tenders, focusing specifically on the building and construction sector. Analyzing 164 Italian public tenders using a protocol based on the GPP toolkit developed by the European Commission, the authors conducted a comprehensive content analysis to investigate the prevalence, distribution, and correlation of green criteria within the sample. The findings indicate a restrained utilization of green criteria, primarily embedded as technical specifications and award criteria. A case study of an innovative building project in Norway by Magnus et al. (2018) [24] highlights the challenges in implementing Green Public Procurement (GPP) due to a disconnect between policy requirements and formal governance.

While research on SPP and ESG is being conducted diversely in countries around the world, the situation in South Korea is relatively underdeveloped in this field on a global scale, with scarce research available, and notably, some existing research is not published in English. This serves as the starting point for our case study.

We initiated the data collection process by compiling a comprehensive list of services ordered over the past three years, resulting in a dataset comprising 427,224 services. To refine the dataset for our study, we focused on national institutions, resulting in a list of 60,539 services. We subsequently excluded services associated with private contracts, unit price contracts, minimum price contracts, and PQ screening, narrowing our focus to services utilizing the proposed bidding method. This meticulous process culminated in a final selection of 21,573 services.

Our study centers on the dependent variable termed the "influence index of the social responsibility evaluation criteria." This variable measures the extent to which social responsibility evaluation criteria impact the overall proposal evaluation score. The proposal evaluation process typically consists of two components: technology evaluation and price evaluation, which collectively add up to 100 points. Technology evaluation is further decomposed into quantitative (assessing creditworthiness and performance) and qualitative (evaluating participants' understanding of and approach to service) aspects. The influence index quantifies the influence of social responsibility evaluation criteria relative to the combined impact of technology and price evaluation. It is calculated by taking the difference between the maximum and minimum values of the social responsibility evaluation criteria distribution and applying the distribution ratio of technology to price evaluation. This calculation results in the ratio of social responsibility evaluation criteria to the total proposal evaluation score.

Our independent variables encompass factors associated with social responsibility evaluation criteria, including the following:

Our study integrates various control variables to account for potential moderating effects, including the following:

Our dataset encompasses a comprehensive compilation of services ordered over the last three years, amounting to a total of 427,224 services. This extensive dataset serves as the foundation for our investigation. However, we progressively refined it to focus on national institutions, resulting in a subset of 60,539 services. Subsequent to eliminating services associated with private contracts, unit price contracts, minimum price contracts, and PQ screening, we arrived at a carefully selected final dataset comprising 21,573 services. This dataset is representative of our study's scope and objectives

To gain insight into the characteristics of our dataset, we conducted an initial analysis, presenting essential summary statistics. This includes the calculation of means, standard deviations, and minimum and maximum values, which offer an overview of the distribution of critical variables.

While exploring our dataset, we examined potential relationships between variables through preliminary analyses. These exploratory insights set the stage for our more in-depth inferential analysis and regression modeling, which we discuss in subsequent sections.

In this section, we present the general characteristics of the primary variables under examination. Our sample consisted of 250 survey targets (100.0%). When considering the distribution by year, the majority of services were procured in 2020, accounting for 57.6% (144), followed by 2019 at 25.2% (63), and 2021 at 17.2% (43). Procurement classification revealed that central procurement was dominant at 74.4% (186), significantly surpassing self-procurement at 25.6% (64). In terms of service period, 47.2% (118) of services fell within the category of 6 months to 1 year, followed by 25.6% (64) for 3 to 6 months, 9.2% (23) for under 3 months and over 2 years, and 8.8% (22) for 1 to 2 years. Regarding estimated price, services with a value of less than 100 million won constituted the majority at 37.2% (93), with less than 50 million won to 100 million won at 21.2% (53), more than 1 billion won at 17.2% (43), less than 50 million won at 14.4% (36), and the lowest category, less than 50 million won, represented at 10.0% (25).

In the context of the social responsibility evaluation criteria, we examined the number of items within the evaluation criteria, with three items being the most common at 82.0% (205), followed by two items at 16.8% (42), and one item at 1.2% (3). Additionally, evaluation criteria were primarily standalone items, accounting for 78.8% (197), with a smaller proportion integrated into other factors at 21.2% (53). When assessing the inclusion of sincerity items, 50.8% (127) of services included them, slightly more than the 49.2% (123) that did not. Lastly, in terms of the evaluating agency, self-evaluation was predominant at 66.8% (167), while the Public Procurement Service's evaluation accounted for 33.2% (83).

In this section, we analyze the influence index, a central variable in our study, while considering various general characteristics. The overall influence index was found to have an average value of 3.88±1.49, with a distribution range spanning from a minimum value of 0.48 to a maximum value of 6.00.

Pearson correlation analysis was employed to explore the relationships between various factors and the overall influence index, a central variable in this study. The analysis encompassed both general service characteristics related to social evaluation criteria and characteristics of social responsibility evaluation criteria. Additionally, it considered factors such as year, procurement classification, service period, estimated price, and characteristics of the social responsibility evaluation criteria, including the number of evaluation criteria items, location of evaluation criteria organization, inclusion of sincerity items, and the evaluation criteria evaluation agency. This examination also assessed the presence of multicollinearity.

In this section, we examine the moderating effect of several variables, including year, on the relationship between social responsibility evaluation factors and the influence index, which are central to this study. A multiple regression analysis is employed with the influence index as the dependent variable, and independent variables encompass the number of evaluation criteria items, the location of evaluation criteria, the inclusion of sincerity items, and the evaluation criteria evaluation institution. We conduct two regression analyses for each moderation variable, proceeding stepwise to verify the moderation effect.