The prevalence of power laws in the citations to scientific papers

This paper presents some preliminary evidence about the existence of power laws representing the upper tail of the citation distributions among 221 scientific sub-fields or Web of Science categories distinguished by Thomson Scientific within the natural and the social sciences. The main finding is that, in a sample consisting of 767,828 articles published in 1998 with a 5-year citation window, in 181 out of 221 sub-fields (representing approximately 77% of the sample of articles) the existence of a power law cannot be rejected. In most sub-fields, the upper tail that can be represented by a power law is small but captures a considerable proportion of the total citations received. The value of the scale parameter is between 2 and 3 for only 21 sub-fields or 6% of the total, greater than 3 for 114 sub-fields or 67%, and greater than 4 for the remaining 46 sub-fields that represent 27% of the total. The estimation of the parameters of the power laws has been done with a novel procedure for citation distributions that is shown to perform better than the standard maximum likelihood methods in the presence of extreme observations. • The authors acknowledge financial support from the Spanish MEC, Grants SEJ2007-67436, SEJ2007-63098 and SEJ200605710. 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-2008217436.

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