Leiden University’s Centre for Science and Technology Studies (CWTS) has developed a new ranking list based exclusively on bibliometric indicators. In early 2007, the CWTS presented its ranking results for the 100 European universities with the largest number of scientific publications. This ranking list proposes four different indicators, from 2010 an additional fifth one, each resulting in a different ranking. The rankings are compiled every 2 years both for a European and the World-wide ranges.
Indicators and Methodology
The Leiden ranking benefits from all experiences and know-how available at CWTS: very accurate definition and ‘unification’ of universities worldwide; corrections for practically all errors and inconsistencies in the raw publication and citation data; thorough methodology based on 20 years of experience in research performance analysis; multiple-indicator approach. This latter point is very important: on the basis of the same data and the same technical and methodological starting points, different types of impact-indicators can be constructed, for instance one focusing entirely on impact, and another in which also scale (size of the institution) is taken in to account. Rankings based on these different indicators are not the same, although they originate from exactly the same data. Moreover, rankings are strongly influenced by the size-threshold used to define the set of universities for which the ranking is calculated.
|MCS (mean citation score)
|The average number of citations of the publications of a university.
|MNCS (mean normalized citation score)
|The average number of citations of the publications of a university, normalized for field differences and publication year. An MNCS value of two for instance means that the publications of a university have been cited twice above world average.
|PP(top 10%) (proportion of top 10% publications)
|The proportion of the publications of a university that, compared with other publications in the same field and in the same year, belong to the top 10% most frequently cited.
|PP(collab) (proportion of interinstitutional collaborative publications)
|The proportion of the publications of a university that have been co-authored with one or more other organizations.
|PP(int collab) (proportion of international collaborative publications
|The proportion of the publications of a university that have been co-authored by two or more countries.
|PP(UI collab) (proportion of collaborative publications with industry)
|The proportion of the publications of a university that have been co-authored with one or more industrial partners.
|MGCD (mean geographical collaboration distance)
|The average geographical collaboration distance (in km) of the publications of a university, where the geographical collaboration distance of a publication equals the largest geographical distance between two addresses mentioned in the publication’s address list.
Special types of journals
|The journal does not publish in English or it does publish in English but authors are concentrated in one or a few countries, indicating that the journal does not have a strong international scope.
|The journal has only a small number of references to other journals in the Web of Science database, indicating that in terms of citation traffic the journal is only weakly connected to these other journals. This is the case for many journals in the humanities, but also for trade journals and popular magazines.
Size-dependent vs. size-independent indicators
|The Leiden Ranking by default reports size-independent indicators. These indicators provide average statistics per publication, such as a university’s average number of citations per publication. The advantage of size-independent indicators is that they enable comparisons between smaller and larger universities. As an alternative to size-independent indicators, the Leiden Ranking can also report size-dependent indicators, which provide overall statistics of the publications of a university. An example is the total (rather than the average) number of citations of the publications of a university. Size-dependent indicators are strongly influenced by the size of a university (i.e., a university’s total publication output) and therefore tend to be less useful for comparison purposes.