NPE Literature Review

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Review Process

The review was done as follows:

  • Collect papers from Google Scholar using keyword searches for NPEs, Patent Trolls, etc.
  • Read abstracts
  • Categorize relevent papers & discard irrelevant papers
  • Read select sections, generally either introductions and/or conclusions. Sometimes scan read papers.
  • Scan references in papers, looking for missed papers and frequently cited economics papers

The next steps are:

  • Upload the papers and link them in
  • Review Lerner (2006). This was missed in the Google search, but found in the reference search, and appears sufficiently seminal to deserve an in-depth review
  • Conduct a second key word search through the Haas Library databases for other missed papers.

It should be noted that as a result of the speed with which I would scan a single paper, it is possible that I have misinterpreted some content. Before using a reference, you should check the source actually says what I claim it says. Likewise, this page was written for speed, not for style.

The Review

Defining a troll

The literature that defines NPEs (Non-practicing entities) is, perhaps unsurprisingly, mostly derogatory. Gregory (2006) provides a typical description. Tokic (2012) suggests that trolls hold invalid patents, as does Myers (2006). Likewise, Harkins (2007) discusses "paper patents" which "are directed to prophetic ideas that had issued as patents without the so-called inventors actually building an operable device or proving the device worked for its intended purpose." He then associates them with patent trolls. Lemley (2007) is more balanced, and considers whether universities also meet the definition of patent trolls. He ends by advocating that they should consider social welfare more carefully.

Creating a Market for IP

According the more economic literature, NPEs may be a good thing, as they may increase competition, innovation, lower downstream prices and enhance consumer choice, as Geradin et al. (2012) claim. However, most authors are somewhat neutral. A small literature has explored the role of NPEs in creating a market for intellectual property (IP). This includes Hagiu and Yoffie (2011), Wang (2010), Pohlmann and Opitz (2010), and Merges (2009), as well as more descriptive contributions from McDonough III (2006) and Abril and Plant (2007). The market for ideas papers explore questions like "What accounts for the relative differences between these different patent intermediation models? ", "Can patent intermediaries make the market more liquid, or will the inefficiencies persist? ", and "What are the efficiency implications of the emergence of these intermediaries for the patent market and society at large? ", as in Hagiu and Yoffie (2011), who conclude that patent intermediaries have so far failed to achieve meaningful scale, but that there are reasons to worry about inefficiencies for small firms, large operating companies and end-consumers. Wang (2010) distinguishes between offensive and defensive aggregators, and claims the former will be first to fall to directed legislation, while the latter will evolve in standard-setting and licensing bodies. Pohlmann and Opitz (2010) reviews just five cases to find that while patent trolls are an efficient way to enforce IPR, their enforcement leads to excessive royalty fees. And Merges (2009) says "All the evidence points to a major incidence of rentseeking, mixed in with the emergence of a perhaps valuable market for independent ideas and inventions.". In work related to the market for ideas, Lu (2011a) claims that NPEs may deliberately assemble portfolios of complements. As such NPEs may act to reduce the anti-commons problem associated with patent thickets. And Beron and Kinsella (2011) suggests that problem of litigation costs for startups might be mitigated by 3rd party litigation.

Differences in Patents and Enforcement

One important question is how the patents and the enforcement of patent rights vary between NPEs and regular firms. In empirical work Shrestha (2010) finds that "NPEs in fact hold high value patents and do not engage in frivolous litigation as has been alleged by their critics". Similar findings are reported in Miller (2011) who says, "I am surprised to find as much evidence as I have supporting those who argue that NPEs serve a useful role in the patent system and generally do not assert weaker patents then those asserted by other litigation claimants. The evidence suggests NPEs may in fact assist foreigners and individuals in collecting the rewards they are entitled to by current patent law." Though Miller (2011) also warns that NPEs seem to litigate patents with broad claims, business method patents, and patents on emerging technologies more frequently than their practicing counterparts. Risch (2011) is even more supportive of NPEs, saying "There is no uniform story about NPE patents or where they come from. While some are business methods patents, most are not. While some litigated patents come from failed start-ups, most did not. While some patents were initially assigned to licensing NPEs, most were not. Indeed, some extremely large companies - and even the federal government - have turned to the very same NPEs to enforce some patents. Some patents enforced by NPEs are invalid, while most are not. NPEs litigate patents with objective indicia that are similar to other litigated patents and appear to be invalidated about as often as other litigated patents, so long as they are not repeatedly asserted." He concludes by saying "There is one marked difference, however. Individuals may face a significant disadvantage in high-stakes patent litigation unless they allow NPEs to enforce their patents. This means that NPE litigation may be the best way for garage inventors to capitalize on their patents if infringers refuse to license." Fischer and Henkel (2009) suggest that NPE patents are actually of high quality and have a high likelihood of being held up in court. They hint at the endogenous selection of patents into an NPE’s portfolio, but are more concerned with potential inefficiencies that might arise by separating the market for patents from the market for technologies.

On the issue of settlements and royalties, Layne-Farrar and Schmidt (2009) claim that "there is no justification for the presumption that non-integrated patent holders always charge higher royalties than vertically integrated companies. Moreover, even when non-integrated patent holders charge ’higher’ royalties than their vertically integrated counterparts, it does not imply that the rates are ’excessive’ or that the firm is exhibiting troll-like behavior. Rather, non-integrated patent holders naturally require higher royalty earnings because they earn no profits downstream and receive no payments in kind in the form of cross-licenses." Likewise, Mazzeo et al. (2011) provides evidence that settlement to patent trolls might not be excessive. Using a sample of settlements that are not related to trolls (or at trolls aren’t identified), they report that "... it does not appear that a systematic or pervasive problem of excessive patent damage awards exists." They also note that "[o]ver 75 percent of the variation in observed patent award levels can be explained by the assembled information about the cases, litigants, and patents-at-issue. As a result, infringement awards can be said to be highly predictable. Large awards are not excessive outliers with respect to the empirical analysis in this study." Reitzig et al. (2006, 2007) use a more theoretical approach to argue that troll settlements are excessive.

Love (2011) finds that NPEs litigate at a much later point in a patent’s term than practicing entities, and suggests that shortening patent terms might be beneficial. Related papers include Allison et al. (2010) who consider litigation frequency (NPEs are frequently involved in litigation), and Lu (2011b) who consider royalty rates (NPEs charge royalty rates that are not different from practicing companies). Liang (2010) consider whether NPEs forum shop and finds evidence that they do.

Other Fairy-tale Monsters

A sub-branch of the NPE literature compares Trolls with other fairy-tale creatures: Giants, like Microsoft and Apple; Dwarves, who are "firms with a large presence in one market, entering another for which they have few or no relevant patents"; ‘David’s, independent inventors or startups who go up against Goliaths; and Sharks, which were the patent trolls of the 19th century, who bought up and exploited agricultural patents. Papers in this literature include: Cooper Feldman and Ewing (2011), Layne-Farrar (2012), Chien (2008) and Magliocca (2006). Chien (2010) documents a patent "arms race" and contrasts it with a "market-place" paradigm. In doing so, he describes many aspects of the complex patent ecosystem. Morgan (2008) suggests that NPEs account for only about 2% of patent lawsuits, and actually play a fairly balanced role in the patent ecosystem.

Judicial Reform and Other Legal Considerations

The law literature has focused mainly on judicial reform and whether NPE infrigement cases should fall under the property rule or the liability rule. Farrand et al. (2011) and Helm and Lee (2008) tackle judicial reform in the patent system related to NPEs and Jones (2006) considers NPEs head on. Likewise there is a large sub-literature that considers the impact of the eBay/Merx decision from the Superb Court, which effective prevents NPEs, as well as many other inventors, from seeking injunctive relief. Typical papers include Eddings (2005), Golden (2006), Mersino (2007) and Maughan (2012). Helm (2006) explains that Pharmaceutical firms supported the NPE position because the injunctive relief differentially affects different industries ability to innovate, and Casagrande (2006) suggests that true problem at issue was business method patents and the Supreme Court’s decision missed the mark. Other judicial reform papers include Chan and Fawcett (2005), who considers the 2005 Patent Reform Act; Reitzig et al. (2006) who argues that courts make unrealistic trade-offs in cases involving NPEs (and should be stricter); and Ferrill (2004) who suggests the creation of Patent Investment Trusts. On whether the property rule or the liability rule is appropriate, and whether the liability rule can be contracted around, Sichelman (2011) and Lemley (2011) provide seminal comments. Finally, Hricik (2010) who considers the ethics of representing each side (and suggests the ethical quandary is in representing the infringer, not the NPE).

NPE References

  • Abril, P.S. Plant, R. 2007. The patent holder’s dilemma: buy, sell, or troll? Communications of the ACM, vol. 50 (1), pp. 36-44. pdf
  • Allison, J.R., Lemley, M.A., Walker, J. 2010. Patent quality and risk aversion among repeat patent litigants. pdf
  • Beron, B.L. Kinsella, J.E. 2011. David vs. goliath patent cases: A search for the most practical mechanism of third party litigation financing for small plaintiffs. N. Ky. L. Rev., vol. 38, pp. 605-687.
  • Casagrande, T.L. 2006. The reach of ebay inc. v. mercexchange, llc: Not just for trolls and patents. Hous. Law., vol. 44, pp. 10-11. pdf
  • Chan, J. Fawcett, M. 2005. Footsteps of the patent troll. Intell. Prop. L. Bull., vol. 10, p. 1. pdf
  • Chien, C.V. 2008. Of trolls, davids, goliaths, and kings: Narratives and evidence in the litigation of high-tech patents. NCL Rev., vol. 87, p. 1571. pdf
  • Chien, C.V. 2010. From arms race to marketplace: The new complex patent ecosystem. Hastings Law Journal, vol. 62. pdf
  • Chuang, A. 2006. Fixing the failures of software patent protection: Deterring patent trolling by applying industry-specific patentability standards. S. Cal. Interdisc. LJ, vol. 16, p. 215. pdf
  • Cooper Feldman, R. Ewing, T. 2011. The giants among us. pdf
  • Eddings, R. 2005. Trolls and titans take fight to top court. Loy. Consumer L. Rev., vol. 18, p. 503. pdf
  • Cotropia, C.A. 2009. The individual inventor motif in the age of the patent troll. Yale JL & Tech., vol. 12, p. 52. pdf
  • Diessel, B.H. 2007. Trolling for trolls: The pitfalls of the emerging market competition requirement for permanent injunctions in patent cases post-ebay. Mich. L. Rev., vol. 106, p. 305. pdf
  • d’Incelli, G. 2008. Has ebay spelled the end of patent troll abuses-paying the toll: The rise (and fall) of the patent troll. U. Miami Bus. L. Rev., vol. 17, p. 343. pdf


  • Farrand, J.R., Shapiro, V.C., Abbott, P.A., Stothers, C.M., Weisberg, S.D., Killworth, R.A. 2011. Judicial reform of patent litigation in the usa. Journal of Intellectual Property Law & Practice, vol. 6 (6), pp. 381-395. pdf
  • Ferrill, E.D. 2004. Patent investment trusts: Let’s build a pit to catch the patent trolls. NCJL & Tech., vol. 6, p. 367. pdf
  • Fischer, T. Henkel, J. 2009. Patent trolls on markets for technology-an empirical analysis of trolls’ patent acquisitions. pdf
  • Geradin, D., Layne-Farrar, A., Padilla, A.J. 2012. Elves or trolls? the role of non-practicing patent owners in the innovation economy. Industrial and Corporate Change, vol. 21 (1), pp. 73-94. pdf
  • Golden, J.M. 2006. Patent trolls and patent remedies. Tex. L. Rev., vol. 85, p. 2111. pdf
  • Gregory, J.K. 2006. Troll next door, the. J. Marshall Rev. Intell. Prop. L., vol. 6, p. i. pdf
  • Hagiu, A. Yoffie, D. 2011. Intermediaries for the ip market. pdf
  • Harkins, C.A. 2007. Fending off paper patents and patent trolls: A novel cold fusion defense because changing times demand it. Alb. LJ Sci. & Tech., vol. 17, p. 407. pdf
  • Helm, J.S. 2006. Why pharmaceutical firms support patent trolls: The disparate impact of ebay v. mercexchange on innovation. Mich. Telecomm. & Tech. L. Rev., vol. 13, p. 331. pdf
  • Helm, K.A. Lee, G.W. 2008. Call it a comeback: A sweeping change in the law on declaratory judgment actions against patent owners. NYU Ann. Surv. Am. L., vol. 64, p. 231. pdf
  • Hricik, D. 2010. Legal ethics and non-practicing entities: Being on the receiving end matters too. Santa Clara Computer & High Tech. LJ, vol. 27, pp. 793-793.
  • Jones, M. 2006. Permanent injunction, a remedy by any other name is patently not the same: How ebay v. mercexchange affects the patent right of non-practicing entities. Geo. Mason L. Rev., vol. 14, p. 1035. pdf
  • Layne-Farrar, A. 2012. The brothers grimm book of business models: A survey of literature and developments in patent acquisition and litigation. pdf
  • Layne-Farrar, A.S. Schmidt, K. 2009. Licensing complementary patents:‘patent trolls’, market structure, and ‘excessive’royalties. pdf
  • Lemley, M. 2011. Contracting around liability rules. pdf
  • Lemley, M.A. 2007. Are universities patent trolls. Fordham Intell. Prop. Media & Ent. LJ, vol. 18, p. 611. pdf
  • Liang, M. 2010. The aftermath of ts tech: The end of forum shopping in patent litigation and implications for non-practicing entities. Tex. Intell. Prop. LJ, vol. 19, pp. 29-419. pdf
  • Love, B. 2011. An empirical study of patent litigation timing: Could a patent term reduction decimate trolls without harming innovators? pdf
  • Lu, J. 2011a. The economics and controversies of nonpracticing entities (npes): How npes and defensive patent aggregators will change license market.
  • Lu, J. 2011b. Have non-practicing entities (npe’s) been overcompensated?
  • Luman III, J.F. Dodson, C.L. 2006. No longer a myth, the emergence of the patent troll: Stifling innovation, increasing litigation, and extorting billions. Intell. Prop. Tech. LJ, vol. 18, pp. 1-1. pdf
  • Magliocca, G.N. 2006. Blackberries and barnyards: Patent trolls and the perils of innovation. Notre Dame L. Rev., vol. 82, p. 1809. pdf
  • Maughan, E. 2012. Protecting the rights of inventors: How natural rights theory should influence the injunction analysis in patent infringement cases. Geo. JL & Pub. Pol’y, vol. 10, pp. 215-321.
  • Mazzeo, M., Hillel, J., Zyontz, S. 2011. Excessive or unpredictable? an empirical analysis of patent infringement awards. pdf
  • McDonough III, J.F. 2006. Myth of the patent troll: An alternative view of the function of patent dealers in an idea economy, the. Emory LJ, vol. 56, p. 189. pdf
  • Merges, R.P. 2009. The trouble with trolls: Innovation, rent-seeking, and patent law reform. Berkeley Tech. LJ, vol. 24, pp. 1583-1647. pdf
  • Mersino, P.M. 2007. Patents, trolls, and personal property: Will ebay auction away a patent holder’s right to exclude. Ave Maria L. Rev., vol. 6, p. 307. pdf
  • Miller, S. 2011. Patent ‘trolls’: Rent-seeking parasites or innovation-facilitating middlemen? pdf
  • Morgan, M. 2008. Stop looking under the bridge for imaginary creatures: A comment examining who really deserves the title patent troll. Fed. Cir. BJ, vol. 17, p. 165. pdf
  • Myers, D. 2006. Reeling in the patent troll: Was ebay v. mercexchange enough. J. Intell. Prop. L., vol. 14, p. 333. pdf
  • Pohlmann, T. Opitz, M. 2010. The patent troll business: An efficient model to enforce ipr? pdf
  • Rantanen, J. 2007. Slaying the troll: litigation as an effective strategy against patent threats. pdf
  • Reitzig, M., Henkel, J., Heath, C. 2006. On sharks, trolls, and other patent animals:‘being infringed’as a normatively induced innovation exploitation strategy. In Available at SSRN, vol. 885914. pdf
  • Reitzig, M., Henkel, J., Heath, C. 2007. On sharks, trolls, and their patent prey: Unrealistic damage awards and firms’ strategies of ’being infringed’. Research Policy, vol. 36 (1), pp. 134-154. pdf
  • Risch, M. 2011. Patent troll myths. Seton Hall Law Review. pdf
  • Shrestha, S. 2010. Trolls or market-makers? an empirical analysis of non-practicing entities. pdf
  • Sichelman, T. 2011. Purging patent law of ‘private law’ remedies. pdf
  • Tokic, S. 2012. The role of consumers in deterring settlement agreements based on invalid patents: The case of non-practicing entities. Stan. Tech. L. Rev., vol. 2012, pp. 2-3. pdf
  • Wang, A.W. 2010. Rise of the patent intermediaries. Berkeley Tech. LJ, vol. 25, pp. 159-1955. pdf

Underlying Economics

Below are the most cited economic papers included in the references of the NPE papers in this review. I have grouped them into three groups. In the first group is the literature that outlines markets for technologies, the existence and characteristics of patent thickets, the suggests that patents are 'probabilistic' (perhaps arising from failures at the patent office). Also included in this group is Josh Lerner's "Trolls on State Street" paper, which was very heavily referenced, and provides the seminal reference for the economic concept of a troll (as far as I can see). I will review Josh's paper shortly.

In the second group, are the broader references that back up the first group. The same themes are present, but generally less developed. Also included in this group is some key papers from the patent pools literature and the litigation of patents literature (the economic branch of it anyway). These two literatures are complementary to the NPE literature but distinct from it. They also build off the papers in the first group. And in the third group is the 'classics'. These are universally referenced and fundamental building blocks.

I estimate that the five most cited papers in the literature (all included in the first group) are:

  • Arora et al. (2001)
  • Gans and Stern (2010)
  • Lemley and Shapiro (2005)
  • Lemley and Shapiro (2007)
  • Lerner (2006)

Market for Technologies, Patent Thickets, and Probabilistic Patents

  • Arora, A., Fosfuri, A., Gambardella, A., 2001. Markets for Technology: The Economics of Innovation and Corporate Strategy. MIT Press, Cambridge, MA.
  • Arora, A. and M. Ceccagnoli (2006), ‘Patent protection, complementary assets, and firm’s incentives for technology licensing,’ Management Science, 52(2), 293-308.
  • Farrell, J. and C. Shapiro (2008). "How Strong Are Weak Patents?" American Economic Review, 98:4, pp. 1347-1369.
  • Gilbert, R., Shapiro, C., 1990. Optimal patent length and breadth. RAND Journal of Economics 21, 106-112.
  • Gans, J.S. and S. Stern (2010) "Is there A Market for Ideas?" Industrial and Corporate Change, 19(3), pp. 805-837.
  • Hall, B. and R. Ziedonis (2001), ‘The patent paradox revisited: an empirical study of patenting in the U.S. semiconductor industry, 1979-1995,’ RAND Journal of Economics, 32(1), 101-128.
  • Lemley, M., 2000. Rational Ignorance at the Patent Office, Berkeley Program in Law and Economics Working Paper Series, 19.
  • Lemley, M.A. and C. Shapiro (2005) "Probabilistic Patents," Journal of Economic Perspectives, Vol. 19(2), pp. 75-98.
  • Lemley, M., & C. Shapiro. 2007. Patent Holdup and Royalty Stacking. 85 Tex. L. Rev. 1991.
  • Lerner, J. (2006): Trolls on State Street? The Litigation of Financial Patents, Working Paper p.1976-2005.
  • Merges, R. (2005), ‘A transactional view of property rights,’ Berkeley Technology Law Journal, 20(4), 1477-1520.
  • Shapiro, C. (2001) "Navigating the Patent Thicket: Cross Licenses, Patent Pools, and Standard Setting," in A. Jaffe, J. Lerner, and S. Stern, eds., Innovation Policy and the Economy, Vol. 1, (Cambridge, MA: MIT Press), 119-150.
  • Shapiro, C. (2006), ‘Injunctions, Hold-Up, and Patent Royalties,’ Working paper, http:// (last accessed August 2010).
  • Ziedonis, R., 2004. Don’t fence me in: fragmented markets for technology and the patent acquisition strategies of firms. Management Science 50, 804-820.

Innovation, Industry Structure, and Patent Scope, Licensing, and Pools

  • Farrell, J., H. Monroe and G. Saloner (1998), ‘The vertical structure of industry: systems competition versus component competition,’ Journal of Economics and Management Strategy, 7(2), 143-182.
  • Jaffe, A. B. (2000), ‘The U.S. patent system in transition: policy innovation and the innovation process,’ Research Policy, 29(4), 531-557.
  • Jaffe, A. B. and J. Lerner (2004) Innovation and Its Discontents: How Our Broken Patent System is Endangering Innovation and Progress, and What to Do About It, Princeton, N.J.: Princeton University Press.
  • Kortum, S., Lerner, J., 1999. What is behind the recent surge in patenting? Research Policy 28 (1), 1-22.
  • Lamoreaux, N.R. and Sokoloff, K. L., 1999. Inventive activity and the market for technology in the United States, 1840-1920. NBER Working Paper 7107, National Bureau of Economics Research, Inc, Cambridge, MA.
  • Lanjouw, J.O., Lerner, J., 2001. Tilting the table? The predatory use of preliminary injunctions. The Journal of Law and Economics XLTV, 573-603.
  • Lanjouw, J., & M. Schankerman. 2001. Characteristics of Patent Litigation: A Window on Competition. The RAND Journal of Economics 32(1):129-151.
  • Lerner, J. and J. Tirole (2004), "Efficient Patent Pools," American Economic Review 94 (2004), 691-711.
  • Lerner, J., M. Strojwas and J. Tirole (2007) "The Design of Patent Pools: The Determinants of Licensing Rules," Rand Journal of Economics 38(3), pp. 610-625.
  • Lerner, Josh. "Patenting in the Shadow of Competitors." Journal of Law and Economics 38 (1995).
  • Lerner, J., 1994. The importance of patent scope: an empirical analysis. Rand Journal of Economics 25 (2), 319-333.
  • Lerner, J. (2002), ‘Where does state street lead? A first look at finance patents, 1971 to 2000,’ The Journal of Finance, 57(2), 901-930.
  • Lanjouw, J., Schankerman, M., 1997. Stylized Facts of Patent Litigation: Value, Scope and Ownership. NBER Working Paper No. 6297.
  • Merges, R.P., Nelson, R.R., 1990. On the complex economics of patent scope. Columbia Law Review 90, 839-916.
  • Macdonald, S., 2004. When means becomes ends: considering the impact of patent strategy on innovation. Information Economics and Policy 16, 135-158.
  • Shapiro, C. (2003) "Antitrust Limits to Patent Settlements," Rand Journal of Economics 34, 391- 411.
  • Schmidt, K. (2006), ‘Licensing Complementary Patents and Vertical Integration,’ Working paper,¼944169 (last accessed November 2006).
  • Schankerman, M., Scotchmer, S., 2001. Damages and injunctions in the protection of intellectual property. RAND Journal of Economics 32, 199-200.

Classic Literature

  • Arrow, K.J., 1962. Economic welfare and the allocation of resources for invention. In: Nelson, R. (Ed.), The Rate and Direction of Inventive Activity. Princeton University Press, Princeton, NJ
  • Coase, R.H. (1932), The Nature of the Firm, JL Econ. \& Org. Vol. 4, 1988
  • Cohen, W.M., Nelson, R.R., Walsh J. P., 2000. Protecting Their Intellectual Assets: Appropriability Conditions and Why US Manufacturing Firms Patent (or Not), NBER Working Paper No. 7552, National Bureau of Economics Research, Inc, Cambridge, MA.
  • Levin, R.C., A.K. Klevorick, R.R. Nelson, and S.G. Winter. 1987. Appropriating the Returns from Industrial Research and Development. Brookings Papers on Economic Activity 3:783-820.
  • Teece, D.J., 1986. Profiting from technological innovation: Implications for integration, collaboration, licensing and public policy. Research Policy 15, 285-305.
  • Williamson, Oliver (1979), "Transaction-Cost Economics: The Governance of Contractual Relations", Journal of Law and Economics, Vol. 22, No. 2. (Oct.), pp. 233-261