Jointly published by Akadémiai Kiadó, Budapest Scientometrics and Springer, Dordrecht DOI: 10.1007/s11192-009-2178-0 Received December 9, 2008 Address for correspondence: JOSÉ A. N. F. GOMES E-mail: jfgomes@fc.up.pt 0138–9130/US $ 20.00 Copyright © 2009 Akadémiai Kiadó, Budapest All rights reserved A comparison of Scopus and Web of Science for a typical university ELIZABETH S. VIEIRA, JOSÉ A. N. F. GOMES Requimte/Departamento de Química, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto, Portugal For many years, the ISI Web of Knowledge from Thomson Reuters was the sole publication and citation database covering all areas of science thus becoming an invaluable tool in bibliometric analysis. In 2004, Elsevier introduced Scopus and this is rapidly becoming a good alternative. Several attempts have been made at comparing these two instruments from the point of view of journal coverage for research or for bibliometric assessment of research output. This paper attempts to answer the question that all researchers ask, i.e., what is to be gained by searching both databases? Or, if you are forced to opt for one of them, which should you prefer? To answer this question, a detailed paper by paper study is presented of the coverage achieved by ISI Web of Science and by Scopus of the output of a typical university. After considering the set of Portuguese universities, the detailed analysis is made for two of them for 2006, the two being chosen for their comprehensiveness typical of most European universities. The general conclusion is that about 2/3 of the documents referenced in any of the two databases may be found in both databases while a fringe of 1/3 are only referenced in one or the other. The citation impact of the documents in the core present in both databases is higher, but the impact of the fringe that are present only in one of the databases should not be disregarded as some high impact documents may be found among them. Introduction Until recently, the Web of Science (WoS) was the only source for the assessment scientific output worldwide because of its multidisciplinarity and international coverage. It includes more than 10000 journals and comprises three citation databases: Arts & Humanities Citation Index (with coverage going back to 1975), Social Sciences Citation Index (with coverage going back to 1956) and Science Citation Index Expanded (with coverage going back to 1900) [THOMSON REUTERS, 2008A]. The WoS contains over 38 million records and, each year, over 1.5 million new records and 23 million new cited references from more than 250 disciplines of the sciences, the social sciences and the arts and humanities are introduced [THOMSON REUTERS, 2008B]. Elsevier Science launched in 2004 the database Scopus that can already be considered a good alternative to that of Thomson Reuters. As described by the owners, ; Published online April 16, 2009 Scientometrics, Vol. 81, No. 2 (2009) 587–600