Patent Thicket Literature Review

This page and its sub pages provide the raw materials and derived 'data' for a literature review on patent thickets.

Process of the review

The following steps were followed:

1. An orginal sample of papers was retrieved from journal databases using keyword searches. Journal databases searched included Google Scholar, Proquest, EBSCO, World of Science, JSTOR, and others. Google Scholar provided by far the most papers and now appears to dominate as a journal search tool. Keywords searched included "patent thicket", "anticommons", "Herfindahl", "blocking patents", "infringing", "dense web", "patent network", and others, both individually and in combination with one another. In additional, several papers that cite certain key papers, including Shapiro (2001), Ziedonis (2004), Hall et al. (2012), were also searched. This process yielded 251 papers that spanned economics, management, public policy, law, computer science, the physical sciences, and policy reports by government or NGOs. 2 papers were added to this list following a recommendation from Peter.
2. Papers were classified into 'Core', 'Up', and 'Down' groups (these are defined below) using word frequency counts for the term "patent thickets" in conjunction with a manual review. The manual review was performed very quickly - papers were not even 'scan' read, just glanced over with a mean review time of around 1 minute per paper. As such there will likely be some classification errors. Specifically, it is expected that some Core papers will turn out to not be core, but I do not anticipate that much if any mis-classification in the opposite direction. 50 papers were discarded during this classification as they were not sufficiently relevant. This left 203 papers.
   1. The Core group consisted of 59 papers that explicitly discuss patent thickets. They might be theory papers that describe mechanisms for thickets, empirical papers that show the existance or lack of existance of thickets, or other papers that provide direct work on thickets.
   2. The Down group consisted of 47 papers that underpin the thicket literature while not explicitly discussing thickets. This group includes theory models for complementary or substitute innovations, for sequential innovation, for 'probabilistic patents', or for patent races, discussions of the relative importance of various aspects of intellectual property (such confering rents vs. providing information), and econometric papers on the use of patent statistics.
   3. The Up group consisted of 97 papers that use patent thickets in some fashion. This group essentially takes patent thickets as given and builds from there. This groups consists of papers concerning mechansisms for addressing the consequences of thickets, such as Pools, SSOs and Standardization, Licensing arrangements, Trolls, Clearance Houses, Joint Ventures, and so forth; papers on IPR Reform, which advocate changes to patent policy, antitrust policy, the Bayh-Dole Act, etc.; papers on firm strategy, which includes strategic responses to thickets, the effects of thickets on portfolio values, and other advocation of firm-level responses; and a considerable amount of industry specific commentary. This last category generally overlaps with the others - for examples there are papers written for genome researchers informing them of the consequences of thickets in thier area, or that patents on segments of the genome are either invalid or not blocking.
3. A convergence process was undertaken. 45 of the 59 Core papers could be 'ripped' to text files and were. The references from these files were then extracted in 41 instances. The remaining 4 papers were law papers with their references scattered in footnotes that could not be reliably extracted by computer software. The references for these 41 papers were then matched against on another to produce counts of the most cited papers within the core group. This process led to 313 papers that were cited by more than one paper in the core group. Of these 239 were not in the original sample of 251. Each of these 239 papers was briefly checked to see whether it should be added to the core group and 8 papers were added.