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 review process consists of the following steps:

1. An #Original Sample of papers was retrieved from journal databases
2. These papers were very quickly classified into #Core, Up, and Down Groups. This classification is undoubtedly subject to errors.
3. The Core group of papers were used to undertake a #Convergence Process
4. Additional core papers, indentified in the Convergence Process were added to the sample
5. All papers were manually classified into groups and #BibTeX Entry Tagging was performed

We are currently conducting step 5 of this process.

Original Sample

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.

Core, Up, and Down Groups

Papers need to be classified into 'Core', 'Up', and 'Down' groups (these are defined below).

The classification in step 2 was performed 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 many classification errors.

Specifically, it is expected that some Core papers will turn out to not be core, but I anticipate less mis-classification in the opposite direction. 50 papers were discarded during the step 2 classification as they were not sufficiently relevant. This left 203 papers. Many more paper may be deemed insufficiently relevant later, but a record of discards should be kept.

The Core Group

The core group consists 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. Papers in this group will generally used the term 'thicket' very frequently.

There were origininally 59 papers classified as core in step 2 of the process. Once stage 5 of the process is completed, each core paper will be reviewed in detail and get its own page on this site.

=The Down Group

The down group consists of 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.

It is not necessary for papers in the down group to even mention patent thickets. Much of the older work (pre-2000) won't because the term didn't exist. This make classifying papers into the down group difficult without area specific expertise. 47 papers were classified as being in the down group in step 2 of the process. However, the convergence process provided many other candidates.

The Up group

The up group consists of paper that use patent thickets in some fashion. This group essentially takes patent thickets as given and builds from there.

At a first take it appears that this groups consists of papers concerning:

• 'Mechansisms for addressing the consequences of thickets: SSOs and Standardization, Licensing arrangements, Trolls, Clearance Houses, Joint Ventures, and so forth.
• IPR reform: advocating changes to patent policy, antitrust policy, the Bayh-Dole Act, etc.
• Firm strategy: strategic responses to thickets, the effects of thickets on portfolio values, and other advocation of firm-level responses
• 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. A considerable number of papers fall into this category and they shouldn't be discarded. It is important to determine which industries have commented on patent thickets, and whether or not they regard them as a problem for industry practitioners.

There were 97 papers classified into the up group in stage 2 of the process, and I expect this number to rise.

Convergence Process

A convergence process was undertaken using the 59 papers that were deemed to be in the core group in step 2 of the process. 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 papers were then matched against one 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.