Patent Citations—An Analysis of Quality Differences and Citing Practices in Hybrid Corn

Abstract

A growing empirical literature uses patent citations as a quality-adjusted measure for innovation, despite concerns about the validity of this measure. This paper links patents with objective measures of improvements in the quality of patented inventionsmeasured through performance in field trials for hybrid cornto examine three potential factors that influence citations: 1) improvements in performance 2) citing practices of patent attorneys, and 3) citing practices of patent examiners. This analysis reveals that citations are robustly correlated with performance, which confirms that citations are a useful qualityadjusted measure for innovation. The citing practices of patent attorneys and examiners, however, also influence citations. Patent attorneys cite early patents, which help establish the patentability of an invention; this practice may inflate citation counts for early patents, particularly for inventions that have only recently become patentable. Attorneys also add self-citations; our analysis indicates that that selfcitations can be an indicator of follow-on invention. By comparison, examiner-added citations are typically unrelated to improvements in performance or follow-on invention.

Patent citations reexamined

“…Seminal work by Griliches (1981) measured patent counts, and later work weighted such counts by the number of forward citations received by each patent on the view that more important patents receive more references (Trajtenberg, 1990a). Later studies used patent citations to measure private patent value (Lanjouw and Schankerman, 2001;Harhoff et al, 1999), firm market value (Hall, Jaffe, and Trajtenberg, 2005), cumulative innovation (Caballero and Jaffe, 1993;Trajtenberg, Henderson, and Jaffe, 1997), geographic spillovers (Jaffe, Trajtenberg, and Henderson, 1993), technology life-cycles (Mehta, Rysman, and Simcoe, 2010), social importance (Moser, Ohmstedt, and Rhode, 2017), originality (Jung and Lee, 2016), and technological impact (Corredoira and FIGURE 1 TOTAL CITATIONS MADE BY YEAR, DIVIDED BY NUMBER OF BACKWARD CITATIONS MADE BY CITING PATENT Banerjee, 2015). Overall, a search for "patent citations" on Google Scholar (conducted January 1, 2018) returns over 21,000 results.…”

The Hidden Costs of Securing Innovation: The Manifold Impacts of Compulsory Invention Secrecy

“…That most (if not all) of the citations in these data will be examiner-added is also potentially important, and discussed at more length in Appendix A. However, as Moser et al (2017) have shown with more recent data, examiners tend to use the characteristics of an invention (rather than performance) to identify prior art. Presuming this generalizes to the historical period, the citations in this paper are best described as a measure of intellectual proximity and content-driven connections.…”

“…That patent citations in this period come from examiners is also important: as Moser et al (2017) show with modern data, patent examiners use physical traits (rather than performance) to identify patents that should be cited as prior art, which provides reassurance that citations in this paper will be measuring intellectual proximity (even within patent classes, since most specifications include patent class fixed effects) rather than quality or importance.…”

Do Patents Enable Disclosure? Evidence from the Invention Secrecy Act

“…Citation chains represent avenues along which knowledge progressively evolves and diffuses over time. Citation data remain the best available and most used measure to track cumulative innovation in the economic literature (e.g., Belenzon, 2012;Galasso and Schankerman, 2014;Moser et al, 2017;Jaffe and de Rassenfosse, 2017). We follow this literature and use the count of forward citations as our main measure of follow-on inventions.…”