New Leiden Ranking

Loet Leydesdorff loet at LEYDESDORFF.NET
Sat Dec 10 15:18:07 EST 2011

Dear colleagues, 


Using the newly introduced indicator for impact in the Leiden Rankings 2011/2012 <> —the Proportion top-10% publications (PPtop 10%)—one can test differences between institutions statistically using the z-test. Furthermore, one can test whether each university performs above or below expectation. 


An Excel sheet with the test embedded is made available at and an example is elaborated in a short introduction at (coauthored with Lutz Bornmann).


The test was previously used analogously for the Excellence Indicator in the SCImago Institutions Rankings <> ; cf.; Bornmann  <> et al., in press), and can be considered as additional to the stability intervals provided at the webpages of the Leiden Ranking <> . The SCImago Rankings are based on Scopus data, and the Leiden Ranking on Web-of-Science data.


With best wishes, 




Amsterdam School of Communications Research (ASCoR), 
Kloveniersburgwal 48, 1012 CX Amsterdam. 
Tel.: +31-20- 525 6598; fax: +31-842239111
 <mailto:loet at> loet at ;  <> ;  <> 


From: ASIS&T Special Interest Group on Metrics [mailto:SIGMETRICS at LISTSERV.UTK.EDU] On Behalf Of Paul Wouters
Sent: Friday, December 09, 2011 11:58 AM
Subject: [SIGMETRICS] New Leiden Ranking


US still dominates high impact publications in science


The US are still the dominant scientific world power, but new centres of science are emerging. MIT is the university which has the highest citation impact of its publications in the world. Princeton and Harvard take positions two and three. These are some of the findings of the new Leiden Ranking 2011 – 2012 which has been published on the website: <> . The top fifty list consists of 42 US based universities, 2 Swiss (Lausanne at 12 and ETH Zurich at 18), 1 Israeli (Weizmann Institute of Science), 4 British (Cambridge at 31, London School of Hygiene & Tropical Medicine at 33, Oxford at 36 and Durham at 42), and one Danish university (Technical University of Denmark). Aggregated to country level, the US has 64 universities in the top 100 list, the UK 12, and the Netherlands 7. The latter is remarkable given its small size.


The Leiden Ranking 2011-2012 is based on an advanced methodology which compensates for distorting effects due to the size of the university, the differences in citation characteristics between scientific fields, differences between English and non-English publications, and distorting effects of extremely high cited publications. Publications authored by researchers at different universities are attributed to the universities as fractions. This prevents distortion of the ranking by counting these publications multiple times (for each co-authoring university). This distorting effect is often overseen in other global university rankings, which leads to a relative advantage of clinical research and some physics fields in these rankings. This makes clear how sensitive global rankings are to the nitty-gritty of the calculations. 


The Leiden Ranking enables users to choose the criteria on which they wish to compare university performance. The menu offers 3 indicators of impact and 4 indicators of scientific collaboration. When scored on the percentage of their papers produced in collaboration with institutes in different countries, the London School of Hygiene & Tropical Medicine tops the list with more than 50 % of its publications co-authored with other countries.


Although in terms of impact, US universities are still strongest, it is clear that other countries are emerging as centres of science by looking at the total production (number of publications in the Web of Science). In this ranking, Harvard University is number one. But in the top 25 we also see universities from Canada (Toronto at 2, British Columbia at 22), Japan (Tokyo at 4, Kyoto at 11, Osaka at 25), Brazil (Sao Paulo at 8), United Kingdom (Cambridge at 13, Oxford at 14, University College at 17), South Korea (Seoul at 19), and China (Zhejiang at 20).


The Leiden Ranking is the first global university ranking which has published the details of its methodology and indicators. The indicators are presented in combination with stability intervals, an advanced statistical method to measure to what extent the differences in rankings between universities are significant.


If one wishes to compare the university citation impact in a global context, it is best to take the percentage of papers in the top 10 % highly cited papers together with the calculation method “fractional counting”. This is the method which compares across institutions and fields in the fairest way.


The Leiden Ranking is based on data of the Web of Science. Data on the arts and humanities are not included since these fields are not well represented in the Web of Science. The Leiden Ranking exclusively measures the citation impact of research of the 500 largest universities in the world. This prevents an arbritrary combination of performance in education, valorization and research, a disadvantage of many global university rankings.


More information about the ranking results and its methodology: <> .


With regards

Paul Wouters
Professor of Scientometrics
Director Centre for Science and Technology Studies
Leiden University

Visiting address: 
Willem Einthoven Building
Wassenaarseweg 62A
2333 AL Leiden
Mail address: P.O. Box 905
2300 AX Leiden
T: +31 71 5273909 (secr.)
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E: p.f.wouters at

CWTS home page:
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