Dikdas Bantara Jurnal DIKDAS BANTARA Vol. No. , pp. 39-54 | p-ISSN: 2615-4285, e-ISSN: 2615-5508 https://journal. id/index. php/dikdasbantara LITERATUR REVIEW: IMPLEMENTATION OF FLIPPED LEARNING FOR ELEMENTARY SCHOOL MATHEMATICS LEARNING IN THE PERIOD 2019-2025 Abdiyati Ilmiyana1. Ellianawati2. Nuni Widiarti3, and Arif Widiyatmoko4 Department of Elementary Education S2, 2Departement of Physical, 3Department of Chemistry. Department of Natural Science Education. Semarang State University. Indonesia E-mail: 1abdiyatiilmiyana@students. id* , 2 ellianawati@mail. nuniwidiarti@unnes. id , 4 arif. widiyatmoko@mail. Article History: Received: Des, 21 2025. Accepted: Feb, 11 2026. Published: March, 31 2026 ABSTRACT Mathematics learning in elementary schools continues to face challenges related to low conceptual understanding, numeracy literacy, and student learning independence. In response to the demands of 21st-century education and the Merdeka Curriculum, student-centered and technology-based learning models are required. One such approach is Flipped Learning, which shifts content delivery outside the classroom and uses in-class time for active learning activities. This study aims to systematically review research trends and findings related to the implementation of Flipped Learning in elementary school mathematics learning during the 2019Ae2025 period. A Systematic Literature Review (SLR) was conducted on 12 national and international peer-reviewed articles identified through Google Scholar using the Publish or Perish application and analyzed thematically and bibliometrically with VOSviewer. The results indicate that Flipped Learning has a positive impact on studentsAo learning outcomes, conceptual understanding, numeracy literacy, motivation, and learning independence. However, its effectiveness is influenced by teacher readiness, quality of digital learning media, technological infrastructure, and parental support. Overall. Flipped Learning shows strong potential to support innovative mathematics learning aligned with 21st-century skills and elementary education curriculum Keywords: Literature Review. Flipped Learning. Ellementary School. Mathematics Learning Copyright A 2026 The Author (Abdiyati Ilmiyan. This is an open access article under the CC BY-SA license. INTRODUCTION The transformation of 21st-century education emphasizes learnercentered approaches, critical thinking, collaboration, and digital literacy as essential competencies for studentsAo future learning and everyday life (Partnership for 21st Century Skills, 2020. OECD, 2. In primary education, these demands are particularly significant because elementary school represents a foundational stage in developing cognitive abilities, learning independence, and positive learning attitudes (OECD, 2. Mathematics, as a core subject, plays a strategic role in fostering logical reasoning, problem-solving skills, and numeracy 32585/dikdasbantara. 7807 | 39 Abdiyati Ilmiyana et al | Literatur Review: Implementation Of Flipped Learning For Elementary School Mathematics Learning In The Period 2019-2025. Vol. 9 No. , page 39-54. competencies essential for studentsAo academic success and daily life (National Council of Teachers of Mathematics [NCTM], 2. Mathematics learning in elementary schools is importance but continues to face significant challenges. Classroom practices remain largely teachercentered and procedural, emphasizing memorization rather than conceptual This condition results in passive learning and limited development of higher-order thinking skills among students (Widya et al. , 2022. Rohmatulloh et , 2. As a result, a gap persists between 21st-century educational goals and actual classroom practices. Flipped Learning has emerged as an instructional approach that responds to these challenges by reversing conventional learning sequences. Instructional content is delivered outside the classroom through digital media, while face-toface time is utilized for interactive discussions and problem-solving activities (Bergmann & Sams, 2012. Rahman & Kim, 2. The model is grounded in constructivist and self-directed learning theories, positioning students as active participants in knowledge construction and teachers as facilitators (Cevikbas & Kaiser, 2. Empirical studies published between 2019 and 2025 report that Flipped Learning positively impacts elementary mathematics learning, including improvements in conceptual understanding, learning outcomes, numeracy literacy, motivation, and self-efficacy (Widya et al. , 2022. Shindika et al. , 2023. Putri et al. , 2. International research further indicates that this model supports the development of 21st-century skills when implemented through well-designed digital instructional media (Al-Harbi, 2023. Sen, 2. A review of previous systematic reviews and meta-analyses shows that most studies examine Flipped Learning in secondary or higher education contexts and focus primarily on general learning outcomes (Rahman & Kim, 2021. Cevikbas & Kaiser, 2. Limited attention has been given to synthesizing research specifically within elementary school mathematics education. In addition, prior reviews rarely integrate bibliometric mapping to identify research trends, dominant themes, and methodological patterns across studies. This situation reveals the need for a comprehensive synthesis that combines systematic review and bibliometric analysis within the specific context of elementary mathematics Based on this identified gap, the central research question of this study is: How has Flipped Learning been implemented and investigated in elementary school mathematics education during the 2019Ae2025 period, and what evidence exists regarding its effectiveness, research trends, and implementation 32585/dikdasbantara. 7807 | 40 Abdiyati Ilmiyana et al | Literatur Review: Implementation Of Flipped Learning For Elementary School Mathematics Learning In The Period 2019-2025. Vol. 9 No. , page 39-54. To answer this question, this study aims to: . analyze methodological trends and research characteristics. examine the impact of Flipped Learning on learning outcomes, conceptual understanding, numeracy literacy, motivation, and learning independence. identify supporting factors and implementation constraints reported across studies. The findings are expected to contribute theoretically to the development of innovative, technology-based mathematics learning models and practically to support teachers and policymakers in designing instruction aligned with 21st-century educational demands. METHODS This study employed a Systematic Literature Review (SLR) to systematically identify, evaluate, and synthesize empirical research related to the implementation of Flipped Learning in elementary school mathematics The SLR approach was selected because it enables a structured, transparent, and replicable synthesis of research findings within a clearly defined scope and time frame (Latifah, 2. To strengthen the analysis of research trends, this study also incorporated bibliometric analysis using VOSviewer to visualize keyword co-occurrence networks and thematic development patterns in the literature. The review focused on national and international journal articles published between 2019 and 2025. This time frame was chosen to capture recent developments in technology-based and post-pandemic learning innovations in elementary education. The review was guided by four research questions: . What methodological characteristics and research trends characterize studies on Flipped Learning in elementary school mathematics during 2019Ae2025? . How is Flipped Learning implemented in elementary mathematics instruction? . What impacts does Flipped Learning have on learning outcomes, conceptual understanding, numeracy literacy, motivation, and learning independence? and . What supporting factors and implementation challenges are reported in the The literature search was conducted using the Google Scholar database with the assistance of the Publish or Perish application to ensure systematic retrieval and citation filtering. The Boolean search string applied was (AuFlipped LearningAy or AuFlipped ClassroomA. and (AuMathematics LearningAy or AuMathematics EducationA. and (AuElementary SchoolAy or AuPrimary SchoolA. , with publication years limited to 2019Ae2025. Only peer-reviewed journal articles available in full-text form were considered. The initial search identified a total of . si jumlah awa. After removing duplicate records and screening titles and abstracts for 32585/dikdasbantara. 7807 | 41 Abdiyati Ilmiyana et al | Literatur Review: Implementation Of Flipped Learning For Elementary School Mathematics Learning In The Period 2019-2025. Vol. 9 No. , page 39-54. relevance, . si jumla. articles were excluded. Full-text eligibility assessment was then conducted, resulting in the exclusion of . si jumla. articles due to mismatched educational level, non-mathematics focus, or incomplete empirical The final number of studies included in this review was . si jumlah akhi. Article selection was guided by predefined inclusion and exclusion criteria to ensure analytical rigor. Studies were included if they examined the implementation of Flipped Learning or Flipped Classroom in elementary or primary school mathematics contexts, were empirical in nature, published between 2019 and 2025, and available in full-text peer-reviewed journal format. Studies conducted at secondary or higher education levels, conceptual papers, opinion articles, theses, conference proceedings, and studies not specifically focused on mathematics learning were excluded from the analysis. Data from the selected studies were extracted using a structured classification table containing information on authorship, publication year, country of study, research objectives, research design, sample characteristics, learning media used, key findings, and reported implementation challenges. The extracted data were analyzed descriptively to summarize research characteristics and methodological trends and thematically to identify patterns of implementation, reported impacts, and recurring constraints. In addition, bibliometric mapping using VOSviewer was conducted to identify dominant keywords, thematic clusters, and the overall development of research trends related to Flipped Learning in elementary mathematics education. The overall review process adhered to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyse. framework to ensure transparency and systematic reporting. The stages included identification, screening, eligibility assessment, and final inclusion of studies. The results of the screening process based on inclusion and exclusion criteria are summarized in Table 1. 32585/dikdasbantara. 7807 | 42 Abdiyati Ilmiyana et al | Literatur Review: Implementation Of Flipped Learning For Elementary School Mathematics Learning In The Period 2019-2025. Vol. 9 No. , page 39-54. Table 1. Article Inclusion and Exclusion Criteria Aspect Inclusion Criteria Exclusion Criteria Articles published in the period Articles published Year of publication 2019Ae2025 The research was conducted at the junior Educational context elementary school level (SD) high, high school, or college level. Focus on other subjects Focus on mathematics learning with Field of study . cience, language, social the Flipped Learning model studies, etc. Non-peer-reviewed Peer-reviewed and full text available articles, abstract only. Publication type scientific articles otherwise inaccessible Opinion Empirical research, classroom action, nonTypes of researchor systematic literature review related to Flipped Learning Written Publication language Written in Indonesian or English language other than those two languages Does not mention Completeness of Presenting clear learning outcomes, relevant methods or methods, and context In addition to the systematic literature review process, bibliometric analysis was conducted to map research trends based on publication year, research focus, research subjects, and methodological characteristics. Bibliometric approaches are widely used to visualize research development and identify dominant themes in educational studies through network mapping and keyword co-occurrence analysis using tools such as VOSviewer (Hanifah et al. , 2022. Iriyani et al. , 2. The integration of systematic review procedures and bibliometric mapping in this study aims to provide a more comprehensive understanding of research patterns and thematic evolution. The overall research flow is presented in Figure 1. 32585/dikdasbantara. 7807 | 43 Abdiyati Ilmiyana et al | Literatur Review: Implementation Of Flipped Learning For Elementary School Mathematics Learning In The Period 2019-2025. Vol. 9 No. , page 39-54. ASearch for selected research articles from Google Scholar. Open Alex. Crossef during 2019-2025 from the results of the search for published on perish (N = 2635 article. Identificatio AIdentify relevant article titles, abstracts, and keywords Filtering AAssess full text articles for eligibility AEligible (N=. AAnalyze the included full-text articles (N = . Eligibility ASummarizing the included full-text articles . articles considered in the analysi. Including Figure 1. Flowchart Prism Diagram RESULTS AND DISCUSSION RESULT A bibliometric analysis was conducted using Publish or Perish (PoP) search results to categorize the selected studies based on publication year . 9Ae2. , research focus, methodological design, and key findings. Visualization of research trends was performed using VOSviewer to identify keyword co-occurrence networks and thematic clusters within Flipped Learning research in elementary mathematics education. The publication trend analysis indicates a consistent increase in the number of studies between 2019 and 2025, reflecting growing academic attention to technologyintegrated and student-centered instructional models at the primary education level. This upward trend aligns with recent bibliometric studies reporting a shift toward interdisciplinary approaches and digital-based learning innovation in elementary education (Lismaya et al. , 2025. Trenggono & Winarni, 2. 32585/dikdasbantara. 7807 | 44 Abdiyati Ilmiyana et al | Literatur Review: Implementation Of Flipped Learning For Elementary School Mathematics Learning In The Period 2019-2025. Vol. 9 No. , page 39-54. Figure 2. Flipped Learning Publication Trends in Elementary School Mathematics Learning . 9Ae2. Figure 2 presents the annual publication trend of Flipped Learning research in elementary school mathematics during the 2019Ae2025 period. To complement the annual publication trend analysis, a keyword co-occurrence network visualization was generated using VOSviewer to identify dominant research themes and their interrelationships within Flipped Learning studies in elementary mathematics education. This mapping provides a structural overview of thematic development and highlights how research focus has evolved across the 2019Ae2025 The visualizationof figure 3 helps identify central keywords, cluster formations, and emerging directions in the literature. Figure 3 : Overview of the study Figure 3 illustrates several interconnected thematic clusters. The dominant cluster centers on instructional models and classroom approaches, indicating that the primary focus of research remains the implementation of Flipped Learning 32585/dikdasbantara. 7807 | 45 Abdiyati Ilmiyana et al | Literatur Review: Implementation Of Flipped Learning For Elementary School Mathematics Learning In The Period 2019-2025. Vol. 9 No. , page 39-54. A second cluster relates to learning outcomes and cognitive dimensions, including conceptual understanding, creative thinking, and academic A third cluster emphasizes digital learning media and technological platforms, reflecting the integration of online learning environments and Learning Management Systems. Another emerging cluster highlights methodological approaches, particularly systematic reviews and quantitative research designs. The network structure demonstrates a gradual shift from exploratory implementation studies toward optimization of technology integration and the strengthening of 21st-century competencies in elementary mathematics To clarify the dominant terms identified in the network visualization. Table 2 presents the main keywords and their contextual meanings within Flipped Learning research in elementary mathematics education. The keywords are determined based on their text size and central position in the map, reflecting their thematic significance and research orientation. Table 2. Keywords and Their Meanings Main Keywords Meaning in the context of research Being the most dominant word : indicates that the main research focus is the application of learning models in the classroom. Demonstrates the learning approach used in the flipped classroom Classroom approach Widely used in literature analysis studies that review the Literature review effectiveness of flipped learning. Mathematics Focus on the application of flipped classroom in the context of mathematics learning. Leading to the effect of flipped learning on students' creative Creative thinking thinking skills. Realistic Indicates the integration of realistic approaches in flipped learning. Classroom model Beyond thematic mapping and keyword prominence, the reviewed studies were further analyzed based on their methodological rigor to deepen the interpretative synthesis. This classification revealed three dominant methodological categories: experimental . ncluding true experimenta. , quasiexperimental, and systematic literature review designs. Experimental studies particularly those employing control group comparisons and statistical testing provided the strongest empirical evidence of effectiveness. These studies consistently reported significant improvements in studentsAo mathematical conceptual understanding, posttest achievement, numeracy literacy, and 32585/dikdasbantara. 7807 | 46 Abdiyati Ilmiyana et al | Literatur Review: Implementation Of Flipped Learning For Elementary School Mathematics Learning In The Period 2019-2025. Vol. 9 No. , page 39-54. classroom engagement compared to conventional instruction. Reported effect sizes ranged from moderate to high, indicating substantial instructional impact when Flipped Learning was implemented with structured pre-class digital preparation and interactive in-class activities. Quasi-experimental studies likewise demonstrated positive outcomes, including enhanced motivation, self-confidence, and independent learning skills. However, variations in sample size, intervention duration, and contextual constraints slightly limited the generalizability of these findings. Classroom action research and descriptive studies further supported the practical classroom benefits of Flipped LearningAiespecially in increasing student participation and improving the learning atmosphereAialthough these designs provided comparatively weaker causal evidence. Meanwhile, systematic literature reviews synthesized findings across multiple contexts and confirmed the overall positive influence of Flipped Learning, yet their conclusions depended on the methodological quality of the primary studies analyzed. The comparative synthesis across methodological categories indicates a consistent pattern of effectiveness. Stronger causal evidence primarily emerges from experimental designs, while quasi-experimental and classroom-based studies highlight practical applicability in authentic educational settings. Similar positive impacts on cognitive and non-cognitive outcomes were observed across diverse research designs and national contexts. A summary of the characteristics, methodologies, and key findings of the selected studies is presented in Table 3. Table 3 Results and Discussion of Flipped Learning Researcher and Year Maslahah MathEd 2 Innovation . Title Research Methods Research Results Flipped Classrooms Implementation of the Descriptive Flipped Classroom success is Learning Model in influenced by teacher. Mathematics Lessons parent collaboration, but for Grade V Elementary is hampered by time School variations in student Flipped Classroom The Effect of the Systematic Flipped Classroom Literature Review school Model (SLR) Mathematical Literacy . Ae30 point. , learning 32585/dikdasbantara. 7807 | 47 Abdiyati Ilmiyana et al | Literatur Review: Implementation Of Flipped Learning For Elementary School Mathematics Learning In The Period 2019-2025. Vol. 9 No. , page 39-54. Researcher and Year Title Research Skills in Schools Methods Research Results Elementary independence . Ae40%), and self-efficacy. Learning Journal 48 % and the Flipped Classroom with Descriptive Education completion of learning a Scientific Approach quantitative (One and Teaching Assisted by WhatsApp Shot Case Stud. significantly with positive student responses. Elementary Google Classroom- True students' understanding JIPMat Assisted Flipped experimental of mathematical concepts . Classroom on . osttest only increased Quadrilaterals control grou. with a high effect size . Implementing The learning outcomes Flipped Classroom and self-confidence of Quasi experiment Model to Improve fourth grade elementary JIIP . on-equivalent Student Learning control grou. Outcomes and Selfhigher than conventional Confidence Flipped Classroom Altered Flipped Classroom in Classroom Action Peddas Elementary School Research students' mathematics . Mathematics Learning cycle. learning outcomes during the COVID-19 pandemic. Flipped Learning Shautut Flipped Learning in Literature study encourages independent Tarbiyah Cultivating Student . hematic learning through self. Learning Independence analysi. regulation and parental Develop a two-phase Flipped Classroom: learning framework . utInnovation in Learning TAUGHT Conceptual of-class and in-clas. Environment . literature review according Arrangement characteristics of digital Mathematics Learning era students. The Influence of the Flipped Classroom FARABI Flipped Classroom Quasi experiment . Learning Model on Elementary School students' mathematical 32585/dikdasbantara. 7807 | 48 Abdiyati Ilmiyana et al | Literatur Review: Implementation Of Flipped Learning For Elementary School Mathematics Learning In The Period 2019-2025. Vol. 9 No. , page 39-54. Researcher and Year Title Research Students' Mathematical Conceptual Abilities Methods Research Results conceptual abilities from the lower grades. The integration of flipped Characteristics of the Systematic IJEMST Mobile Problem-Based Literature Review learning. PBL Learning Flipped (PRISMA) improves digital literacy Classroom (MPBLFC) and critical thinking. Gamified Flipped The Effect of Gamified Learning Flipped Learning on Quasi experiment improves 11 EJEL . Fifth Graders' (ANCOVA) school students' learning Mathematics Achievement and engagement. European Flipped LearningAeSTEM The Implementation of Systematic Journal Flipped Learning Model Literature Review 12 Educational and STEM Approach in & Research literacy, and 21st-century Elementary Education analysis . Based on the findings summarized in Table 3. The overall synthesis reveals that Flipped Learning contributes not only to improved cognitive outcomes such as conceptual understanding and numeracy literacy but also to non-cognitive development, including motivation, engagement, and self-regulated learning. The effectiveness of implementation is influenced by instructional design quality, digital media integration, teacher readiness, parental support, and technological Discussion This review demonstrates a consistent pattern of positive outcomes associated with the implementation of Flipped Learning in elementary mathematics education. However, rather than merely reiterating descriptive findings, this discussion interprets the results through methodological comparison and theoretical positioning. Across the analyzed studies, stronger causal claims emerge primarily from experimental and true experimental designs, which employed control groups and statistical testing. These studies provide the highest level of empirical evidence, reporting moderate to high effect sizes in improving conceptual understanding, posttest achievement, numeracy literacy, and classroom engagement. Quasi-experimental designs reinforce these findings but 32585/dikdasbantara. 7807 | 49 Abdiyati Ilmiyana et al | Literatur Review: Implementation Of Flipped Learning For Elementary School Mathematics Learning In The Period 2019-2025. Vol. 9 No. , page 39-54. present slightly lower generalizability due to contextual and sampling variations. Meanwhile, classroom action research offers practical classroom validation, and systematic literature reviews function as confirmatory evidence across broader This layered evidence structure strengthens the robustness of the overall conclusion and addresses concerns regarding methodological depth. From a theoretical perspective, the findings extend active learning theory and constructivist learning principles by demonstrating how structured pre-class digital preparation enhances cognitive readiness and optimizes in-class higherorder learning activities. The flipped structure shifts instructional time from passive knowledge transmission to guided conceptual application, problemsolving, and collaborative reasoning. Beyond cognitive gains, the model contributes to self-regulated learning development, aligning with selfdetermination theory by increasing learner autonomy, competence, and Thus, the theoretical contribution of this study lies in positioning Flipped Learning not merely as a technological innovation, but as a pedagogical restructuring model that integrates cognitive activation, motivational reinforcement, and digital mediation in elementary mathematics learning. Nevertheless, the effectiveness of Flipped Learning is highly contextdependent. Technology access remains a critical limitation, particularly in regions with unstable internet connectivity or limited device ownership. Teacher digital literacy and instructional design competence significantly influence implementation quality. Cross-country variations observed in the reviewed studies indicate differences in infrastructure readiness, curriculum alignment, and parental involvement, which may affect learning outcomes. Therefore, generalization of results must be approached cautiously, especially when applying findings from technologically advanced contexts to developing educational These contextual constraints highlight that instructional design quality and systemic readiness are decisive factors in determining instructional impact. Overall, this synthesis demonstrates converging empirical evidence supporting the effectiveness of Flipped Learning in improving both cognitive and non-cognitive outcomes in elementary mathematics education. The strongest causal support derives from controlled experimental research, while quasiexperimental and classroom-based designs reinforce ecological validity within authentic learning environments. By integrating methodological comparison, theoretical articulation, and contextual analysis, this study moves beyond a purely descriptive review and offers a more rigorous, evidence-based interpretation of Flipped Learning implementation. This layered analytical approach enhances the 32585/dikdasbantara. 7807 | 50 Abdiyati Ilmiyana et al | Literatur Review: Implementation Of Flipped Learning For Elementary School Mathematics Learning In The Period 2019-2025. Vol. 9 No. , page 39-54. credibility, depth, and transferability of the studyAos conclusions across diverse elementary education contexts. CONCLUSION This study systematically synthesized national and international research on the implementation of Flipped Learning in elementary mathematics education from 2019 to 2025 using a Systematic Literature Review approach combined with bibliometric mapping. Through the analysis of methodological characteristics, thematic clusters, and empirical findings, this review provides both structural and evidential insight into the development of Flipped Learning research. The findings reveal a consistent upward trend in publications and a shift toward technology-integrated and interdisciplinary approaches. Strongest causal evidence emerges from experimental studies, while quasi-experimental and classroom-based research reinforce practical applicability across diverse contexts. Collectively, the evidence confirms that structured pre-class digital preparation and interactive in-class engagement significantly improve conceptual understanding, numeracy literacy, motivation, and self-regulated learning in elementary mathematics. Theoretically, this study positions Flipped Learning as a pedagogical restructuring model that integrates active learning, constructivist engagement, and digital mediation. However, effectiveness remains context-dependent, influenced by teacher digital competence, infrastructure readiness, and socioeducational support systems. Future research should prioritize context-sensitive experimental designs and longitudinal evaluations to strengthen evidence-based implementation across varied educational environments. In addition, this review underscores the importance of aligning pedagogical innovation with systemic educational readiness. The successful implementation of Flipped Learning in elementary mathematics education requires not only instructional redesign but also institutional support, professional development for teachers, and equitable access to digital resources. Policymakers and school leaders should consider structured capacity-building programs and infrastructure enhancement to ensure sustainable adoption. Future research should further explore longitudinal impacts, comparative cross-country analyses, and adaptive models integrating emerging technologies such as artificial intelligence and personalized learning systems to refine and contextualize Flipped Learning practices in diverse elementary education settings. 32585/dikdasbantara. 7807 | 51 Abdiyati Ilmiyana et al | Literatur Review: Implementation Of Flipped Learning For Elementary School Mathematics Learning In The Period 2019-2025. Vol. 9 No. , page 39-54. ACKNOWLEDGEMENT The researchers wish to convey their heartfelt appreciation to Semarang State University for its invaluable support in facilitating the completion of this study. The institutionAos academic environment and resources have greatly contributed to the research process. The authors are also sincerely grateful to all student participants who willingly and enthusiastically shared their experiences, insights, and time, which have been essential in enriching the data and strengthening the overall findings of this DECLARATION Author Contributions All authors contributed substantially to this study. The first author was responsible for conceptualization, data collection, and initial drafting of the manuscript. The second author contributed to methodology design and data analysis. The third author supported validation, supervision, and critical revision of the manuscript. All authors reviewed and approved the final version of the manuscript. Funding Statement This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors. Conflict of Interest The authors declare that there are no conflicts of interest, either financial or non-financial, related to this study. Additional All data analyzed in this study are derived from published Information articles and are publicly accessible. No new primary data involving human or animal subjects were collected. Further information regarding the study can be obtained from the corresponding author upon reasonable request. REFERENCES