Patent citation inflation: The phenomenon, its measurement, and relative indicators to temper its effects

Highlights

• Patent citation inflation has occurred frequently over the past four decades – in some cases at very high levels.

• A deep exploration of the phenomena of citation inflation using USPTO patents as a corpus is conducted.

• Appropriate methods for measuring the impact of two types of patent citation inflation are proposed.

• Several relative indicators that more accurately reflect the worth of citation counts by properly accounting for inflation are developed.

Abstract

In recent decades, the United States Patent and Trademark Office (USPTO) has been granting more and more patents with more and more references, which has led to patent citation inflation. Citation counts are a fundamental consideration in decisions about research funding, academic promotions, commercializing IP, investing in technologies, etc. With so much at stake, we must be sure we are valuing citations at their true worth. In this article, we reveal two types of patent citation inflation and analyze its causes and cumulative effects. Further, we propose some alternative indicators that more accurately reflect the true worth of a citation. A case study on the patents held by eight universities demonstrates that the relative indicators outlined in this paper are an effective way to account for citation inflation as an alternative approach to evaluating patent activity.

Introduction

In economics, it is well known that inflation reflects devaluation, i.e., that purchasing power decreases with excessive growth in the supply of money (Abel & Bernanke, 2005; Barro, 1997). However, when citation inflation occurs, does the same apply? Moreover, if so, how then can an idea’s value be accurately measured with citations? These are indeed important and interesting issues.

Half a century ago, de Solla Price (1961, 1963) proposed that the number of scientific publications would grow exponentially. Although the law of exponential growth in science has not been proven to be entirely correct, scientific research publications are experiencing very rapid growth (Larsen & von Ins, 2010). Patents have undergone similar growth, as evidenced by the increase in patents granted by the United States Patent and Trademark Office (USPTO) over the past several decades. For example, in 1976, the USPTO granted around 70,000 patents, but, by 2015, that number had quadrupled to around 300,000.

Although the external forces that drive patents differ from scientific publications in several respects – for example, economic incentives for R&D, competition, the need for market dominance, or the need to take public ownership of one’s ideas – both patents and scientific articles contain references that provide the potential approach to trace knowledge interactions and technology flows. Further, the mechanisms that generate the references within those outputs have some commonalities. References trace the provenance of knowledge and properly attribute the work of others (Criscuolo & Verspagen, 2008; Jaffe, Trajtenberg, & Fogarty, 2000). Authors, applicants, and patent examiners all conduct thorough searches for relevant references, often deeming an innovation to be novel when they do not find any (Cotropia, Lemley, & Sampat, 2013), and, today, the internet and information retrieval systems make it very easy to conduct exhaustive literature reviews that result in extensive reference lists. Cotropia (2009) and Sampat (2010) pointed out that an abundance of references can benefit patent applicants because their patents might earn the presumption of validity against the cited art in litigation since the examiners might not scrutinize each and every reference in an exhaustive list. Greater output and more references per unit of output would undoubtedly cause an explosion in references with the inevitable result of citation inflation.

In this article, we have chosen to examine patent citation inflation, i.e., citation inflation in a corpus of patents. Although we cannot attest that all our conclusions will hold true for the academic literature, we do believe that some of our findings will apply. Moreover, we hope our overarching purpose shines through, which is to explore the efficacy of traditional research performance indicators given the phenomenon of citation inflation. Hence, for this reason and for brevity, we simply use the term citation inflation throughout this article.

In recent decades, the references in patents have been used extensively to: trace the spread of technical knowledge (Chen & Hicks, 2004; Hu & Jaffe, 2003; Nelson, 2009; Park & Suh, 2013); chart technological trajectories (Epicoco, 2013; Érdi et al., 2013; Huang et al., 2017; Martinelli, 2012); map technical domains (Wang, Zhang, & Xu, 2011; Weng & Daim, 2012); and even to identify untapped opportunities for innovation (Albert, Avery, Narin, & McAllister, 1991; Lanjouw & Schankeman, 2004; Verspagen, 2000; von Wartburg, Teichert, & Rost, 2005). With so many studies relying on patents as a data source, the phenomenon of exploding references has not escaped attention. Hall, Jaffe, and Trajtenberg (2001) highlight that: “The combination of more patents making more citations suggests a kind of citation ‘inflation’ that may mean that later citations are less significant than earlier ones.” They also proposed several methods of tempering the effects of citation inflation (Hall, Jaffe, & Trajtenberg, 2000; Hall et al., 2001; Jaffe & Lerner, 2001; Jaffe & Trajtenberg, 1999). Persson et al. (2004) studied inflation in fundamental bibliometric indicators from the perspective of scientific collaboration, including citations counts, and concluded that relative indicators are needed to guarantee the validity of findings drawn from bibliometric results. Such calls also have peaked concern over inequitable journal impact factors as a result of citation inflation – especially self-citations (Chorus & Waltman, 2016; Heneberg, 2014, 2016; Ioannidis, 2015; Opthof, 2013).

Correctly evaluating the worth of citations is an essential issue because, in the same way that we cannot directly compare the box office takings of a movie released in 1939 with one released in this year, directly comparing the citations received by two pieces of research produced decades apart is just as absurd. Quantitative science & technology evaluation requires measures that are transparent, relatively simple, and free of any bias due to time, discipline, or field. In a very recent work, Petersen, Pan, Pammolli, and Fortunato (2019) provided a solution to the paper citation inflation that arises from growth in scientific publications and/or the increasing length of reference lists. However, patent citation inflation has not yet been addressed from a systematic perspective. With the above problems in mind, we set ourselves three goals:

• To conduct an in-depth exploration of the phenomena of citation inflation using patents as a corpus;

• To identify the different types of citation inflation and devise appropriate methods for measuring the impact of each;

• To develop relative indicators that more accurately reflect the worth of citation counts by properly accounting for inflation.