Each publication of a university belongs to one, or sometimes to more than one, of the above main fields. If a publication belongs to more than one main field, the publication is assigned fractionally to each of the main fields. For instance, a publication belonging to two main fields is assigned to each of the two fields with a weight of 1 / 2 = 0.5.
Publications are assigned to the five main fields using an algorithmic approach. Traditionally, fields of science are defined by sets of related journals. This approach is problematic especially in the case of multidisciplinary journals such as Nature, PLOS ONE, PNAS, and Science, which do not belong to one specific scientific field. The five main fields listed above are defined at the level of individual publications rather than at the journal level. In this way, publications in multidisciplinary journals can be properly assigned to a field.
Publications are assigned to main fields in the following three steps:
After the above steps have been taken, each publication in Web of Science has an assignment to a micro-level field, and each micro-level field in turn has an assignment to at least one main field. Combining these results, we obtain for each publication an assignment to one or more main fields.
The link between subject categories and main fields can be found in this Excel file.
Information on the 4113 micro-level fields is available in this Excel file. For each micro-level field, the file provides the following information:
A visualization of the micro-level fields is provided below. By clicking on the visualization, an interactive version of the visualization will be opened in the VOSviewer software. The visualization can be interpreted as follows:
It should be noted that the micro-level fields play an important role in the calculation of the field-normalized impact indicators in the Leiden Ranking.
CWTS and Thomson Reuters have jointly decided to make the definitions of the micro-level fields publicly available. For each publication in Web of Science in the period 2006–2014 (article and review document types only), the Web of Science accession number (also known as the UT code) is made available along with a link to the micro-level field to which the publication has been assigned. Also, for each publication it is indicated whether the publication has been classified as a core or a non-core publication. If you want to get access to the definitions of the micro-level fields, please briefly tell us about the purpose for which you want to use the field definitions. To do so, please fill out the form below. CWTS and Thomson Reuters won’t share your data with other parties.
For more information on the methodology for the algorithmic construction of the micro-level fields, we refer to a paper by Waltman and Van Eck (2012). The algorithm that is used is called the smart local moving algorithm. This algorithm is documented in a paper by Waltman and Van Eck (2013).