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87 N.C. L. Rev. 1657 (2008-2009)
Patent Citation Networks Revisited: Signs of a Twenty-First Century Change

handle is hein.journals/nclr87 and id is 1667 raw text is: PATENT CITATION NETWORKS REVISITED: SIGNS OF A TWENTY-FIRST CENTURY CHANGET KATHERINE J. STRANDBURG, GABOR CSARDI, JAN TOBOCHNIK, PtTER tRDI, AND LASZLO ZALANYI** This Article reports an empirical study of the network composed of patent nodes and citation links between them. It builds on an earlier study in which we argued that trends in the growth of the patent citation network provide evidence that the explosive growth in patenting in the late twentieth-century was due at least in part to the issuance of increasingly trivial patents. We defined a measure of patent stratification based on comparative probability of citation; an increase in this measure suggests that the United States Patent and Trademark Office is issuing patents of comparatively less technological significance. Provocatively, we found that stratification increased in the 1990s during the patent explosion. Here we report a further study indicating that the trend toward increasing stratification leveled off beginning around 2000. This observation suggests that there was a de facto tightening of patentability standards well before the doctrinal shifts reflected in the Supreme Court's flurry of patent activity beginning around 2005. We also investigate the possibility that changes in our measure of stratification are due to * Copyright © 2009 by Katherine J. Strandburg, Gfbor Csfrdi, Jan Tobochnik, Peter Erdi, and L~szl6 Zal6nyi. ** Katherine J. Strandburg is Professor, DePaul University College of Law and was Visiting Professor, Fordham University School of Law (Fall 2008). G~ibor Cs~rdi is currently a postdoctoral researcher in the Department of Medical Genetics, University of Lausanne, Switzerland. Much of this work was completed while he was a doctoral student at the Department of Biophysics, KFKI Research Institute for Particle and Nuclear Physics of the Hungarian Academy of Sciences, Budapest, Hungary, and Center for Complex Systems Studies, Kalamazoo College. Jan Tobochnik is Dow Distinguished Professor of Natural Science, Department of Physics, Kalamazoo College. Pter lrdi is Henry Luce Professor, Departments of Physics and Psychology, Kalamazoo College, and Head, Department of Biophysics, KFKI Research Institute for Particle and Nuclear Physics of the Hungarian Academy of Sciences, Budapest, Hungary. Liszl6 Zaldnyi is a doctoral student, Department of Biophysics, KFKI Research Institute for Particle and Nuclear Physics of the Hungarian Academy of Sciences, Budapest, Hungary, and Center for Complex Systems Studies, Kalamazoo College. We are grateful to the American Institute of Physics for providing the data we used in the study described in Part II.D.1 of this Article.

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