References made and citations received by scientific articles

This paper studies massive evidence about references made and citations received after a five-year citation window by 3.7 million articles published in 1998-2002 in 22 scientific fields. We find that the distributions of references made and citations received share a number of basic features across sciences. Reference distributions are rather skewed to the right, while citation distributions are even more highly skewed: the mean is about 20 percentage points to the right of the median, and articles with a remarkable or outstanding number of citations represent about 9% of the total. Moreover, the existence of a power law representing the upper tail of citation distributions cannot be rejected in 17 fields whose articles represent 74.5% of the total. Contrary to the evidence in other contexts, the value of the scale parameter is between three and four in 15 of the 17 cases. Finally, power laws are typically small but capture a considerable proportion of the total citations received. Acknowledgements The authors acknowledge financial support from the Spanish MEC, Grants SEJ2007-67436, SEJ2007-63098 and SEJ2006-05710. The database of Thomson Scientific (formerly Thomson-ISI; Institute for Scientific Information) has been acquired with funds from Santander Universities Global Division of Banco Santander. This paper is part of the SCIFI-GLOW Collaborative Project supported by the European Commission’s Seventh Research Framework Programme, Contract no. SSH7-CT-2008-217436.