Patent Citation Networks Revisited: Signs of a Twenty-First Century Change?

39 Pages Posted: 3 Jun 2009

See all articles by Gabor Csardi

Gabor Csardi

Hungarian Academy of Sciences; Kalamazoo College

Jan Tobochnik

Kalamazoo College

Peter Erdi

Hungarian Academy of Sciences; Kalamazoo College - Center for Complex System Studies (CCSS)

Laszlo Zalanyi

Hungarian Academy of Sciences; Kalamazoo College

Katherine J. Strandburg

New York University School of Law

Date Written: June 2, 2009

Abstract

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 USPTO 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 something other than changes in patentability standards. While not conclusive, our results suggest that neither shifts in predominance of technological areas nor changes in citation practice account for our observations. We have thus identified an apparent puzzle: What happened around 2000 to cause a de facto tightening of patentability standards at the USPTO?

Keywords: patent, intellectual property, network

JEL Classification: K39

Suggested Citation

Csardi, Gabor and Tobochnik, Jan and Erdi, Peter and Zalanyi, Laszlo and Strandburg, Katherine J., Patent Citation Networks Revisited: Signs of a Twenty-First Century Change? (June 2, 2009). North Carolina Law Review, Vol. 87, 2009. Available at SSRN: https://ssrn.com/abstract=1413290

Gabor Csardi

Hungarian Academy of Sciences ( email )

Budapest
Hungary

Kalamazoo College ( email )

1200 Academy Street
Kalamazoo, MI 49006
United States

Jan Tobochnik

Kalamazoo College ( email )

1200 Academy Street
Kalamazoo, MI 49006
United States

Peter Erdi

Hungarian Academy of Sciences ( email )

Budapest
Hungary

Kalamazoo College - Center for Complex System Studies (CCSS) ( email )

1200 Academy Street
Kalamazoo, MI 49006-3295
United States

Laszlo Zalanyi

Hungarian Academy of Sciences ( email )

Budapest
Hungary

Kalamazoo College ( email )

1200 Academy Street
Kalamazoo, MI 49006
United States

Katherine J. Strandburg (Contact Author)

New York University School of Law ( email )

40 Washington Square South
New York, NY 10012-1099
United States

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