Citation Topics are algorithmically derived citation clusters (using an algorithm developed by CWTS, Leiden). This is a three-level hierarchical document-level classification system. The three levels of the hierarchy are:
- Macro-topics (10)
- Meso-topics (326)
- Micro-topics (2444)
Named document clusters based on cited and citing relationships between documents.
All documents from 1980-present were algorithmically clustered where possible, based on their cited and citing relationships in a Leiden-type community algorithm. The algorithm includes parameters to enforce clustering and maintain minimum cluster size; cited relationships to pre-1980 documents are included. The full methodology has yet to be published, but information on the type of algorithm can be found in:
Traag, V.A., Waltman, L. & van Eck, N.J. From Louvain to Leiden: guaranteeing well-connected communities. Sci Rep 9, 5233 (2019). https://doi.org/10.1038/s41598-019-41695-z
Documents are only assigned to a single topic.; all document types are considered. Not all documents will have been successfully assigned to a topic, and by default these are not displayed (you can display them using the checkbox in the Research Area filter). Approximately 75% of all documents from 1980 onward are assigned to a topic. This is >90% for article and review document types.
Macro- and meso-topics are manually labeled based on their contents. Micro-topics were algorithmically labeled with their most significant keyword. As Citation Topics are based on citation relationships and not the content or subject matter of their constituent documents, topics are labeled by inference and any name may not be descriptive for every document in the topic.
Each topic is also labeled with a permanent numerical prefix to identify the precise topic. For example, the micro-topic 2.144.321 OLEDs is a sub-topic of the meso topic 2.144 Organic Semiconductors, which is a sub-topic of the macro topic 2 Chemistry.
New documents are added to the existing topics based on their cited references, with each monthly data update. Each year, we perform a full clustering update, which will retain the Citation Topic structure but individual documents may move between micro topics and entirely new micro topics may be added.
- Clinical & Life Sciences
- Agriculture, Environment & Ecology
- Electrical Engineering, Electronics & Computer Science
- Social Sciences
- Engineering & Materials Science
- Earth Sciences
- Arts & Humanities