Three options for citation tracking: Google Scholar, Scopus and Web of Science

Background: Researchers turn to citation tracking to find the most influential articles for a particular topic, and to see how often their own published papers are cited. For years researchers looking for this type of information had only one resource to consult: the Web of Science. In 2004, two competitors emerged – Scopus and Google Scholar. The research reported here uses citation analysis in an observational study examining these three databases; comparing citation counts for articles from two disciplines (oncology and condensed matter physics) and two years (1993 and 2003). Methods: 11 journal titles with varying impact factors were selected from each discipline (oncology and condensed matter physics) using the Journal Citation Reports (JCR). All articles published in the selected titles were retrieved for both years, and a stratified random sample of articles was chosen, resulting in four sets of articles. During the week of November 7-12, 2005 we extracted the citation counts for each research article from the three sources. The actual citing references for a subset of the articles published in 2003 were also gathered from each of the three sources. Results: For oncology 1993, Web of Science returned the highest average number of citations, 45.3. Scopus returned the highest average number of citations (8.9) for oncology 2003. Web of Science returned the highest number of citations for condensed matter physics 1993 and 2003 (22.5 and 3.9 respectively). The data showed a significant difference in the mean citation rates between all pairs of resources except between Google Scholar and Scopus for condensed matter physics 2003. For articles published in 2003, Google Scholar returned the largest amount of unique citing material for oncology and Web of Science returned the most for condensed matter physics. Conclusions: This study did not identify any one of these three resources as the answer to all citation tracking needs. Scopus showed strength in providing citing literature for 2003 oncology articles, while Web of Science produced more citing material for 2003 and 1993 condensed matter physics, and 1993 oncology articles. Unique material was returned by all three tools. Our data indicate that the question of which tool provides the most complete set of citing literature may depend on the subject and publication year of a given article