Ludo Waltman’s research while affiliated with Leiden University and other places

Several initiatives have been taken to promote the open availability of bibliographic metadata of scholarly publications in Crossref. We present an up-to-date overview of the availability of six metadata elements in Crossref: reference lists, abstracts, ORCIDs, author affiliations, funding information, and license information. Our analysis shows that the availability of these metadata elements has improved over time, at least for journal articles, the most common publication type in Crossref. However, the analysis also shows that many publishers need to make additional efforts to realize full openness of bibliographic metadata.

Preprinting has become an increasingly important component of the scholarly communication system, facilitating rapid open dissemination of scientific knowledge. This study investigates the adoption of preprinting over time, focusing on how it varies across scientific disciplines and geographical regions. We analyzed bibliometric data on 4M preprints and 105M peer-reviewed outputs in the period 1991-2023. Peer-reviewed outputs were linked to preprints using data from Dimensions, OpenAlex, and Crossref, resulting in 2.2M peer-reviewed outputs linked to a preprint. Our findings indicate a strong growth in preprinting, with a nearly threefold increase in the number of preprints published between 2017 and 2022. The adoption of preprinting is highest in the physical and mathematical sciences, particularly among researchers in the Americas and Europe. In recent years, preprinting has also increased notably in the information and computing sciences and the life and medical sciences, driven primarily by researchers in North America and Western and Northern Europe. Preprinting remains relatively uncommon in the humanities and the social and behavioral sciences. Asia demonstrates low preprint adoption, with Eastern Asia showing a modest increase in recent years. Preprint adoption in specific disciplines varies significantly across regions, showing that preprint adoption is shaped by the interplay between disciplines and regions.

Preprinting has become an increasingly important component of the scholarly communication system, facilitating rapid open dissemination of scientific knowledge. This study investigates the adoption of preprinting over time, focusing on how it varies across scientific disciplines and geographical regions. We analyzed bibliometric data on 4M preprints and 105M peer-reviewed outputs in the period 1991-2023. Peer-reviewed outputs were linked to preprints using data from Dimensions, OpenAlex, and Crossref, resulting in 2.2M peer-reviewed outputs linked to a preprint. Our findings indicate a strong growth in preprinting, with a nearly threefold increase in the number of preprints published between 2017 and 2022. The adoption of preprinting is highest in the physical and mathematical sciences, particularly among researchers in the Americas and Europe. In recent years, preprinting has also increased notably in the information and computing sciences and the life and medical sciences, driven primarily by researchers in North America and Western and Northern Europe. Preprinting remains relatively uncommon in the humanities and the social and behavioral sciences. Asia demonstrates low preprint adoption, with Eastern Asia showing a modest increase in recent years. Preprint adoption in specific disciplines varies significantly across regions, showing that preprint adoption is shaped by the interplay between disciplines and regions.

Understanding the different ways in which different science mapping approaches capture the structure of scientific fields is critical. This paper presents a comparative analysis of two commonly used approaches, topic modeling (TM) and citation-based clustering (CC), to assess their respective strengths, weaknesses, and the characteristics of their results. We compare the two approaches using cluster-to-topic and topic-to-cluster mappings based on science maps of cardiovascular research generated by TM and CC. Our findings reveal that relations between topics and clusters are generally weak, with limited overlap between topics and clusters. Only in a few exceptional cases do more than one-third of the documents in a topic belong to the same cluster, or vice versa. For TM the presence of highly similar topics is a considerable challenge. A strength of TM is its ability to represent societal needs related to cardiovascular disease, potentially offering valuable insights for policymakers. In contrast, CC excels in depicting the intellectual structure of cardiovascular diseases, with a strong capability to reflect scientific micro-communities. This study deepens the understanding of the use of TM and CC for science mapping, providing insights for users on how to apply these approaches based on their needs.

This mixed-methods study examines the complex interplay of actors and factors shaping research assessment policies in Lithuania in the years 1996–2008, a period of transition towards Western practices. Analysing policy documents, bibliometric data, interviews, and grey literature, we focus on the interactions among policymakers, international experts, providers of publication data, and researchers. Our findings reveal the significant influence of international networks on Lithuanian policymakers, leading to the adoption of quantitative assessment and reliance on Web of Science data. However, this narrow focus, coupled with existing power dynamics and top-down decision-making, led to gamesmanship in publishing practices and conflicts among disciplines, culminating in a Constitutional Court challenge. This research also highlights the substantial role of journal publishers and data providers in influencing policy shifts. We underscore the need for international organisations to adopt open data sources that encompass a wider array of scholarly outputs. Additionally, national policymakers must consider disciplinary differences and research capacity when designing assessment policies. The Lithuanian experience serves as a cautionary tale, emphasising the importance of context-specific, inclusive, and flexible research assessment systems, particularly in light of ongoing reforms such as the Coalition for Advancing Research Assessment (CoARA).

A science map of topics is a visualization that shows topics identified algorithmically based on the bibliographic metadata of scientific publications. In practice not all topics are well represented in a science map. We analyzed how effectively different topics are represented in science maps created by clustering biomedical publications. To achieve this, we investigated which topic categories, obtained from MeSH terms, are better represented in science maps based on citation or text similarity networks. To evaluate the clustering effectiveness of topics, we determined the extent to which documents belonging to the same topic are grouped together in the same cluster. We found that the best and worst represented topic categories are the same for citation and text similarity networks. The best represented topic categories are diseases, psychology, anatomy, organisms and the techniques and equipment used for diagnostics and therapy, while the worst represented topic categories are natural science fields, geographical entities, information sciences and health care and occupations. Furthermore, for the diseases and organisms topic categories and for science maps with smaller clusters, we found that topics tend to be better represented in citation similarity networks than in text similarity networks.

The purpose of this brief is to provide an introduction to an increasingly popular way of communicating outputs of research: the Publish-Review-Curate (PRC) model. This model came into practice in the early 2000s, and it is now beginning to grow more rapidly. Here, we explain the model for the benefit of researchers, research funders, research institutions, and others in the scholarly communication ecosystem, and we provide data on uptake of the model to date.

Performance-based funding systems have significantly impacted the research systems in many countries. This study examines the evolution of the performance-based funding system in Lithuania. Using a multi-level, multi-actor, and multi-issue approach, we investigate how various actors influenced policy choices and outcomes. Through a combination of policy analysis, interviews, and bibliometric analysis, we explore tensions between international aspirations and domestic realities, the interplay between national policies and publishing behaviour, and challenges of metrics-based research assessment. Our findings reveal how the dominant role of scientific elites at all levels of governance had both intended outcomes (increase in publications in general and international publications in particular) and unintended consequences (proliferation of institutional journals and strategic publishing practices). Our study provides insights for policymakers and stakeholders seeking to develop effective and sustainable policies amidst calls for research assessment reform.

This mixed-methods study examines the complex interplay of actors and factors shaping research assessment policies in Lithuania in the period 1996–2008, a period of transition towards Western practices. Analysing policy documents, bibliometric data, interviews, and grey literature, we focus on the interactions between policymakers, international experts, providers of publication data, and researchers. Our findings reveal the significant influence of international networks on Lithuanian policymakers, leading to the adoption of quantitative assessment and reliance on Web of Science data. However, this narrow focus, coupled with existing power dynamics and top-down decision-making, led to unintended consequences and conflicts among disciplines, culminating in a Constitutional Court challenge. This research also highlights the substantial role of journal publishers and data providers in influencing policy shifts. We underscore the need for international organizations to adopt open data sources that encompass a wider array of scholarly outputs. Additionally, national policymakers must consider disciplinary differences and research capacity when designing assessment policies. The Lithuanian experience serves as a cautionary tale, emphasizing the importance of context-specific, inclusive, and flexible research assessment systems, particularly relevant for ongoing reforms such as the Coalition for Advancing Research Assessment (CoARA).