INTRODUCTION

Background and objectives

Hepatology, the study of liver diseases, remains a critical area of research due to the increasing global burden of liver conditions such as viral hepatitis, fatty liver disease, cirrhosis, and hepatocellular carcinoma. These diseases present significant healthcare challenges worldwide, with both developed and developing regions facing unique issues^1-2.

In Western countries, such as the United States and Europe, non-alcoholic fatty liver disease (NAFLD) and alcoholic liver disease (ALD) are leading causes of liver-related morbidity^3-4. Meanwhile, in Asia, viral hepatitis, particularly hepatitis B and C, continues to be a primary concern, contributing to high incidences of liver cancer⁵. South America has seen a growing focus on the epidemiology of liver diseases, particularly related to viral hepatitis and parasitic infections such as schistosomiasis, which heavily affect liver function^6-7.

Reflecting on the global advancements in hepatology over the past 30 years, several key developments stand out:

The number of publications in hepatology surged in 1994 and has remained high since 2009 (CHART 1). Research output has been particularly prolific in countries such as the United States, United Kingdom, Italy, Germany, China, France, and Japan. In South America, Brazil leads in the number of research publications (CHART 2).

Addressing these challenges necessitates international cooperation, given the complex, multifactorial nature of hepatological conditions and the need for a multidisciplinary approach.

Understanding the structure of research collaboration in hepatology is essential to map out how knowledge has advanced and to identify key contributors driving the field forward. Co-authorship network analysis offers valuable insights into the dynamics of collaboration by visualizing relationships between researchers, institutions, and regions. It allows us to assess how central researchers influence the dissemination of knowledge and how emerging collaborations have shaped the field. This analysis is particularly relevant as research collaboration has grown exponentially over the past decades, largely due to the globalization of science and increased access to digital tools that facilitate international partnerships. By studying the patterns of collaboration from 1994 to 2023, this paper aims to illuminate how hepatology research has evolved globally and regionally.

Scope of the study

This study focuses on the analysis of co-authorship networks in the field of Hepatology, based on research articles indexed in the Web of Science (WoS) Core Collection from 1994 to 2023. The data set comprises 9,278 articles, extracted using the keyword “hepatology” as the topic search parameter, ensuring that a comprehensive range of research contributions across different subfields of hepatology is captured. By examining data over 30 years, I aim to explore the changes in collaborative patterns over time, highlighting key researchers, institutions, and regions that have shaped the field.

Significance of the study

The significance of this research lies in its ability to provide a detailed map of hepatology research collaboration over three decades. By identifying major contributors and institutions, we can gain a clearer understanding of the individuals and organizations that have played pivotal roles in advancing liver disease research. Additionally, the study will highlight the development of international collaborations in addressing global liver disease challenges.

This research also evaluates the structural changes within the collaborative networks, revealing how partnerships have shifted in response to new scientific advancements and public health priorities.

By examining these trends, we can assess the impact of collaboration on research productivity and innovation, as well as predict future directions for hepatology research. Furthermore, this analysis underscores the importance of fostering international collaboration, particularly as the field moves towards more personalized approaches to liver disease management and as new technologies such as genomics and machine learning transform clinical practice.

The identification of major research hubs and influential figures within the hepatology network offers a foundation for further exploration of how collaborative research can be strengthened. This research has the potential to inform policymakers, funding agencies, and researchers on how to foster more effective global partnerships to address the pressing issues in liver disease research and treatment.

In summary, this paper provides an in-depth analysis of the evolution of research collaboration in hepatology, highlighting the major researchers, institutions, and cooperative trends over 30 years. This work contributes to the understanding of the current state and future direction of the field, emphasizing the crucial role of international research collaboration in advancing hepatology.

METHODS

Data collection and analytical environment

This study analyzes research collaboration in hepatology from 1994 to 2023, based on 9,278 publications indexed in the WoS Core Collection, retrieved as of October 2024. The search was conducted using the topic keyword “hepatology”. The data includes bibliometric information such as authors, titles, journals, and affiliation details, which were used to construct co-authorship networks.

The extracted data are processed and analyzed using Python programming language (version 3.10.5) within the integrated development environment (IDE) PyCharm (software version 2022.1.3). This data process allows for a comprehensive study of both the structural features and dynamic changes within the hepatology co-authorship network.

Network analysis methods

The following macro-level indicators were used to assess the overall structure of the co-authorship networks:

Macro-level metrics

Network density: the ratio of actual edges in the network to the maximum possible number of edges. This measures the level of connectedness in the network and indicates the overall collaboration intensity between researchers.

Clustering coefficient: this metric evaluates the degree to which nodes (researchers) tend to cluster together, indicating localized collaboration patterns¹¹.

Components: a component is defined as a sub-network in which all nodes are connected either directly or indirectly through edges. The number of components is calculated to understand the fragmentation or connectivity of the overall network¹².

Average path length: the mean shortest path between all pairs of nodes, providing insight into how close researchers are on average across the network¹³.

Micro-level metrics: the following micro-level indicators were used to measure the importance of individual researchers within the co-authorship networks:

Degree centrality:degree centrality measures the number of direct connections each node has to other nodes. Researchers with a high degree centrality are considered well-connected and may play pivotal roles in disseminating knowledge across the network¹².

Closeness centrality: closeness centrality calculates how close a node is to all other nodes in the network, based on the shortest path lengths. Nodes with high closeness centrality are central within the network and can quickly interact with others¹².

Betweenness centrality: betweenness centrality quantifies how often a node appears on the shortest paths between other nodes. Researchers with high betweenness centrality act as important intermediaries in collaboration, facilitating interactions between otherwise unconnected groups¹³.

RESULTS

Network analysis of hepatology research (1994-2003)

The network analysis of hepatology research between 1994 and 2003 reveals several important trends in collaborative efforts. The network density during this period was relatively low at 0.0058, indicating that only a small portion of possible collaborations between researchers were realized (Table 1). However, the average clustering coefficient was remarkably high at 0.9155, suggesting that although the network was sparse, the existing collaborations tended to form tight-knit clusters. The network was highly fragmented, consisting of 338 components (Table 1), reflecting the presence of many isolated sub-networks (Figure 1)¹⁴.

In terms of degree centrality, Lambertini A (0.0621) emerged as the most central node, followed closely by Stroffolini T and several others with similar values (0.0577) (Table 2). These researchers had the highest number of direct connections, indicating their key roles in collaboration during this period. When examining closeness centrality, Trepo C (0.0668) was the most central figure, suggesting that this researcher had the shortest average distance to all other nodes, facilitating efficient collaboration (Table 3). Regarding betweenness centrality, Trepo C again held the top position (0.0169), indicating a crucial role in bridging different research groups and facilitating communication across the network (Table 4).

Network analysis of hepatology research (2004-2013)

The period from 2004 to 2013 showed a further decrease in network density to 0.0008, indicating that, despite increased publication rates, collaborative ties did not keep pace with the growing research landscape (Table 1). The average clustering coefficient remained high at 0.9101, suggesting the continued formation of tightly interconnected groups of researchers. However, the network became even more fragmented, with 765 distinct components, further highlighting the isolated nature of many research collaborations during this time (Figure 2). The average distance between nodes remained infinite, underscoring the highly disconnected nature of the network¹⁴.

Manns, Michael P (0.0250) was the most connected researcher in terms of degree centrality, reflecting his prominence in direct collaborations (Table 2). In closeness centrality, Manns, Michael P again stood out (0.1857), underscoring his central position within the research network (Table 3). Notably, Manns, Michael P also had the highest betweenness centrality (0.0616), indicating that he played a pivotal role in linking otherwise disconnected groups of researchers, serving as a key figure in promoting intergroup collaboration (Table 4).

Network analysis of hepatology research (2014-2023)

In the most recent period from 2014 to 2023, network density continued to decline, reaching 0.0006 (Table 1). This decreasing density trend indicates that, despite the global expansion of hepatology research, direct collaboration among researchers has not proportionally increased. The average clustering coefficient remained high at 0.9116, reflecting strong local collaboration patterns. The number of components increased further to 1302, showing a fragmentation in the research landscape (Figure 3)¹⁴.

Pol, Stanislas (0.0123) emerged as the most connected researcher in terms of degree centrality, highlighting his significant involvement in collaborative efforts (Table 2). In terms of closeness centrality, Berg, Thomas (0.1990) was the most central researcher, suggesting his influential position within the research network (Table 3). Berg, Thomas also had the highest betweenness centrality (0.0282), indicating that he played a crucial role in bridging various research communities and facilitating cross-collaborations between disparate groups (Table 4).

Summary of trends

Over the 30-year period from 1994 to 2023, hepatology research networks have become more fragmented, with increasing numbers of isolated components despite steady levels of clustering within existing collaborations. Key figures, such as Lambertini A, Manns, Michael P, and Berg, Thomas, have consistently occupied central roles within the research networks, serving as hubs of collaboration and linking otherwise disconnected groups of researchers. However, the decreasing network density and increasing number of components reflect challenges in fostering widespread, cohesive collaborations across the global hepatology research community.

DISCUSSION

The analysis of hepatology research networks from 1994 to 2023 reveals several notable trends in collaboration patterns and the evolving structure of global research. Over the three decades analyzed, hepatology research has expanded significantly, both in terms of publication output and the complexity of its collaboration networks (CHART 1). However, the findings indicate that while the volume of research has grown, the density of collaboration among researchers has declined, highlighting challenges in fostering interconnected, large-scale research efforts (Table 1).

Decreasing network density and increasing fragmentation

One of the most striking observations from this study is the consistent decline in network density over time. Between 1994 and 2023, the network density decreased from 0.0058 in the early period to 0.0006 in the most recent decade. This reduction in density suggests that, despite the global growth of hepatology research, direct collaborative ties between researchers have not kept pace. The decline in network density could be attributed to several factors, including the increasing specialization within hepatology subfields, the expansion of the global research community, and the geographical dispersion of researchers.

Moreover, the analysis highlights an increasing fragmentation within the hepatology research network, with the number of components rising from 338 in the 1994-2003 period to 1302 in 2014-2023. This growing fragmentation suggests that many research collaborations are occurring within isolated sub-networks, limiting cross-disciplinary and international partnerships. While local collaborations remain strong, as evidenced by the consistently high clustering coefficient (above 0.91 across all periods), the absence of widespread interconnectedness points to a potential area for improvement. Enhanced communication and collaboration across research clusters could significantly strengthen the field’s ability to address global liver disease challenges. This includes tackling the rising burden of NAFLD and hepatitis C, as well as addressing parasitic infections like schistosomiasis, which are prevalent in regions such as South America.

The role of key researchers

Throughout the study period, certain researchers have emerged as central figures in the hepatology research network. For example, in the early period (1994-2003), Lambertini, A, and Trepo C stood out for their high degree and betweenness centrality, indicating their pivotal roles in bridging different research groups. These researchers acted as connectors, facilitating the flow of information and collaboration between otherwise disconnected parts of the network.

In the subsequent periods (2004-2013 and 2014-2023), researchers such as Michael P Manns and Thomas Berg played similar roles. Manns was central in both degree and betweenness measures, underscoring his influence in promoting international collaboration. His role as a key intermediary between research groups likely contributed to the dissemination of knowledge, particularly in the areas of viral hepatitis and liver transplantation.

Regional and global collaboration trends

The geographical distribution of hepatology research has also evolved. In the earlier periods, research was dominated by Western countries, particularly the United States and Europe, where NAFLD and ALD were primary research areas. In contrast, the Asian region, particularly China, has seen a rapid increase in research output over the last decade, primarily focused on viral hepatitis. This shift in regional focus underscores the global nature of hepatology research, with different regions prioritizing distinct liver disease challenges based on their local epidemiological needs^15-16.

Despite this global expansion, our findings indicate that international collaboration remains limited. Although key figures like Manns and Berg have facilitated some cross-regional partnerships, the overall level of international collaboration is not proportional to the growing burden of liver disease worldwide. For example, while the field has made significant advancements in the treatment of hepatitis C and liver cancer, the lack of broader collaboration networks may slow progress in emerging areas such as personalized liver disease management and addressing liver diseases that pose challenges and problems in different regions of the world, potentially hindering advancements in research.

Implications for future research

This study provides critical insights into the structural dynamics of hepatology research networks, emphasizing the need for more robust and widespread collaboration to address global liver disease challenges. To facilitate this, several strategies could be implemented. First, funding agencies and academic institutions should encourage cross-disciplinary and cross-regional partnerships by prioritizing grants for collaborative projects that span different areas of hepatology. Second, the creation of centralized research hubs or consortia, particularly in regions like Asia and South America where liver disease is prevalent, could enhance the global integration of research efforts. Additionally, it is important for the national societies of internal medicine and gastroenterology to collaborate with each other in research efforts.

Furthermore, fostering collaboration between senior researchers and emerging scientists may help address the growing fragmentation of the field. Early-career researchers should be encouraged to engage in international partnerships, which could be facilitated through initiatives such as researcher exchange programs and joint workshops focused on liver disease.

CONCLUSION

This 30-year comprehensive analysis of research collaboration in hepatology, covering the period from 1994 to 2023, reveals several important trends that have shaped the field. The findings demonstrate that while hepatology research has grown significantly in terms of publication volume, collaboration networks have become increasingly fragmented. The analysis of co-authorship networks shows a consistent pattern of high clustering coefficients across all periods, indicating that collaboration tends to occur in tight-knit groups rather than across the broader research community. However, network density has decreased over time, suggesting that the overall level of collaboration has not kept pace with the rapid expansion of research output.

The most central researchers identified in each decade - such as Lambertini A (Italy) and Trepo C (France) (1994-2003), Manns, Michael P (Germany) (2004-2013), and Berg, Thomas (Germany) (2014-2023) - have played pivotal roles in facilitating connections and driving knowledge dissemination within their respective periods. These researchers acted as key bridges, linking otherwise isolated research groups and fostering communication across the field. The rise of prominent researchers in viral hepatitis and NAFLD highlights the field’s shift in focus toward addressing global public health priorities, particularly the growing burden of lifestyle-related liver diseases.

Despite the increase in publication activity, the growing fragmentation of the research network, evidenced by the rising number of disconnected components, underscores the need for fostering more inclusive and interdisciplinary collaboration. To address the complex and multifactorial nature of liver diseases, a more interconnected and globalized research network is essential. International partnerships, facilitated by central researchers and institutions, will continue to play a crucial role in advancing hepatology research and tackling the pressing challenges in liver disease.

In conclusion, this study underscores the importance of identifying key researchers and fostering greater collaboration to enhance the global effort against liver diseases. As hepatology continues to evolve, future research should aim to reduce fragmentation by promoting more cross-disciplinary and cross-regional cooperation. This will ensure a more cohesive and innovative research landscape, capable of addressing the ever-changing challenges in hepatology.

REFERENCES

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