Patents cited in the scientific literature: An exploratory study of 'reverse' citation relations

This paper reports on a new approach to study the linkage between science and technology. Unlike most contributions to this area we do not trace citations of scientific literature in patents but explore citations of patents in scientific literature. Our analysis is based on papers recorded in the 1996-2000 annual volumes of the CD-Edition of Science Citation Index (SCI) of the Institute for Scientific Information (ISI) and patent data provided by the US Patent and Trademark Office. Almost 30,000 US patents were cited by scientific research papers. We analysed the citation links by scientific fields and technological sectors. Chemistry-related subfields tended to cite patents more than other scientific area. Among technological sectors, chemical clearly dominates followed by drugs and medical patents as the most frequently cited categories. Further analyses included a country-ranking based on inventor-addresses of the cited patents, a more detailed inspection of the ten most cited patents, and an analysis of class-field transfers. The paper concludes with the suggestions for future research. One of them is to compare our 'reverse' citation data with 'regular' patent citation data within the same classification system to see whether citations occur, irrespectively of their directionality, in the same fields of science and technology. Another question is as to how one should interpret reverse citation linkages.     

Bibliometric performance measures

Three different types of bibliometrics — literature bibliometrics, patent bibliometrics, and linkage bibliometric can all be used to address various government performance and results questions. Applications of these three bibliometric types will be described within the framework of Weinberg's internal and external criteria, whether the work being done is good science, efficiently and effectively done, and whether it is important science from a technological viewpoint. Within all bibliometrics the fundamental assumption is that the frequency with which a set of papers or patents is cited is a measure of the impact or influence of the set of papers. The literature bibliometric indicators are counts of publications and citations received in the scientific literature and various derived indicators including such phenomena as cross-sectoral citation, coauthorship and concentration within influential journals. One basic observation of literature bibliometrics, which carries over to patent bibliometrics, is that of highly skewed distributions — with a relatively small number of high-impact patents and papers, and large numbers of patents and papers of minimal impact. The key measure is whether an agency is producing or supporting highly cited papers and patents. The final set of data are in the area of linkage bibliometrics, looking at citations from patents to scientific papers. These are particularly relevant to the external criteria, in that it is quite obvious that institutions and supporting agencies whose papers are highly cited in patents are making measurable contributions to a nation's technological progress.     

What is Special about Patent Citations? Differences between Scientific and Patent Citations

The emergence of pattent bibliometrics as a new branch of scientometrics necessitates a deeper understanding of the relationship between patents and papers. As this connection is established through the linkage between patents and research papers, one must have a clear idea of similarities and differences between patent and paper citations. This paper will investigate to what extent one can not only apply bibliometric methods to patents but also extend the existing interpretative framework for citations in research papers to the field of patent citations. After pointing out some parallels in the debates about the nature of citations in patents and scientific articles, the paper outlines those parts of bibliometric theory covering scientific citations that could be relevant to patent citations too. Then it highlights the specialties and peculiarities of patent citations. One major conclusion is that the general nature of a common framework for both scientific and patent citations would severely limit its usefulness, but research on academic citations might still be a great source of inspiration to the study of patent citations.     

The citation impact of social sciences and humanities upon patentable technology

This paper examines the citation impact of papers published in scientific-scholarly journals upon patentable technology, as reflected in examiner- or inventor-given references in granted patents. It analyses data created by SCImago Research Group, linking PATSTAT’s scientific non-patent references (SNPRs) to source documents indexed in Scopus. The frequency of patent citations to journal papers is calculated per discipline, year, institutional sector, journal subject category, and for “top” journals. PATSTAT/Scopus-based statistics are compared to those derived from Web of Science/USPTO linkage. A detailed assessment is presented of the technological impact of research publications in social sciences and humanities (SSH). Several subject fields perform well in terms of the number of citations from patents, especially Library and Information Science, Language and Linguistics, Education, and Law, but many of the most cited journals find themselves in the interface between SSH and biomedical or natural sciences. Analyses of the titles of citing patents and cited papers are presented that shed light upon the cognitive content of patent citations. It is proposed to develop more advanced indicators of citation impact of papers upon patents, and ways to combine citation counts with citation content and context analysis.

     

Can applied science be ‘good science’? Exploring the relationship between patent citations and citation impact in nanoscience

There is a rich literature on how science and technology are related to each other. Patent citation analysis is amongst the most frequently used to tool to track the strengths of links. In this paper we explore the relationship between patent citations and citation impact in nanoscience. Our observations indicate that patent-cited papers perform better in terms of standard bibliometric indicators than comparable publications that are not linked to technology in this way. More specifically, we found that articles cited in patents are more likely to be cited also by other papers. The share of highly cited papers is the most striking result. Instead of the average of 4% of all papers, 13.8% of the papers cited once or twice in patents fall into this category and even 23.5% of the papers more frequently cited in patents receive citation rates far above the standard. Our analyses further demonstrate the presence and the relevance of bandwagon effects driving the development of science and technology.     

Technological Relevance of Science: An Assessment of Citation Linkages between Patents and Research Papers

Patent citations to the research literature offer a way for identifying and comparing contributions of scientific and technical knowledge to technological development. This case study applies this approach through a series of analyses of citations to Dutch research papers listed on Dutch-invented and foreign patents granted in the US during the years 1987–1996.First, we examined the general validity and utility of these data as input for quantitative analyses of science-technology interactions. The findings provide new empirical evidence in support of the general view that these citations reflect genuine links between science and technology. The results of the various analyses reveal several important features of industrially relevant Dutch science: (1) the international scientific impact of research papers that are also highly cited by patents, (2) the marked rise in citations to Dutch papers on foreign-invented patents; (3) the large share of author-inventor self-citations in Dutch-invented patents; (4) the growing relevance of the life sciences, (5) an increase in the importance of scientific co-operation. We also find significant differences between industrial sectors as well as major contributions of large science-based multinational enterprises, such as Philips, in domestic science-technology linkages.The paper concludes by discussing general benefits and limitations of this bibliometric approach for macro-level analysis of science bases in advanced industrialised countries like the Netherlands.     

Analysis of propensity to patent and science-dependence of large Japanese manufacturers of electrical machinery

Summary The paper aims to clarify the extent to which the results of scientific-oriented research conducted by corporations are reflected in their application-oriented research. Focusing on large Japanese manufacturers of electrical machinery, the paper analyses firm-level data on presentations of scientific papers that represent the results of scientific-oriented research activities, citations of scientific papers in patents, and inventions. The electrical machinery industry, a prototypical science-based industry, has been placing a growing emphasis on scientific-oriented research during the 1990's as is evident from trends in R&D expenses, scientific papers, and inventions. Regression analysis results suggest a complementary relationship between citations of basic scientific knowledge as presented in scientific papers on the one hand and acts of invention on the other hand, in the sense that a rise in citations corresponds to a rise in inventions. Moreover, the results suggest that invention efficiency (number of patent claims per unit of R&D expenditure) has been increasing during the 1990's. Furthermore, the results suggest that, given the exogenous influences on the patent system in Japan, it is necessary to include the number of patent claims when attempting to measure corporate technology development activity through the volume of patent applications. However, there was no finding of a clear relationship between the number of scientific papers and inventions. Implications of these results for corporate R&D strategy are examined.     

Indicators for measuring the impact of scientific citations in patents

Scientific publications cited in patents are fundamental elements to assess the transfer of science to technology. Numerous studies evaluate the impact of references in patents and scientific publications and various measurement methods and indicators are proposed. This article reviewed the existing literature on the indicators used to date to determine their suitability and effectiveness to evaluate the impact of patent citations. For this purpose, we analyzed the characteristics of the studies examined and proposed a qualitative classification of indicators from both a technological (patents) and scientific-academic (scientific articles) perspective. Among the results we find that the use of scientometric indicators is primarily focused on analyzing their relevance for patents through the inclusion of scientific citations. Conversely, the same is not true from the academic point of view where gaps still persist in terms of what the impact is when scientific articles are cited in patents. Among the key conclusions is the diversity of proposals to measure scientific citations in patents, though these are conditioned on bibliographic standardization and metadata management of the patents themselves, making it possible to quantify aspects similar to the immediacy index, impact index, or h-index for authors/inventors, albeit from a technological dimension.     

Linkage between patents and papers: An interim EPO/US comparison

A unification of more than one million non-patent references (NPR's) on the front pages of U.S. and EPO patents has been carried out, with a subsequent match to theScience Citation Index (SCI), in order to investigate the citation linkage between patented technology and the scientific research literature. The U.S. system shows an extremely rapid increase in linkage, with citations from U.S. patents to U.S. authored papers increasing more than three-fold over the last decade. The EPO system does not show any increase; the occurrence of non-patent references appears to be relatively constant in the EPO system over the last decade. In the U.S. system approximately 75 percent of the cited papers originate in public science institutions, showing large dependence of patented industrial technology on public science. We expect to find similar result in the EPO system.     

The growing number of patent citations to scientific papers: Changes in the world,nations, and fields

This study analyzes USPTO patents in the period 1998–2017. The number of science-related patents has increased twice as fast as the number of patents and scientific publications, and the number of cited papers per patent has almost doubled. These results vary substantially from one scientific and technological field to another. The proportion of the research papers cited by a patent has doubled. It refers to papers that are mostly published by the countries that have developed both scientific and technological capability and, surprisingly, are mainly used by inventors abroad. However, a weak relationship between the number of citations received from patents and papers reveals that the assessment of research performance needs some changes as the percentage of papers related to the innovations has grown over time.     

Knowledge-transfer analysis based on co-citation clustering

Based on co-citation cluster analysis, we propose a knowledge-transfer analysis model for any technology field. In this model, patent data with backward citations to non-patent literature and forward citations by later patents would be analyzed. Co-citation clustering of the cited articles defines scientific knowledge sources, while that of the patents themselves defines technology fronts. According to the citation between the article and patent clusters, the landscape of knowledge-transfer including route and strength between scientific knowledge sources and technology fronts can be mapped out. The model has been applied to the field of transgenic rice. As a result of the analysis, ten scientific knowledge sources and eight technology fronts have emerged, and reasonable links between them have been established, which clearly show how knowledge has been transferred in this field.     

Validation study: Patent citations as indicators of science and foreign dependence

The purpose of this study was to test whether the distribution of citations from issued U.S. patents could be used to measure the science dependence and the foreign dependence of patented technologies. The citations considered were front page references from U.S. patents citing to U.S. and foreign patents, to research papers and to other publications. Rankings based on the number of citations per patent to the scientific literature were compared to peer rankings of the science dependence of the technologies. Rankings based on the number of citations to foreign origin material, including foreign origin U.S. patents, foreign patents and foreign priority statements, were compared to peer rankings of the foreign dependence of the technological areas.For the analysis a total of 24 technologies were chosen. Twelve of these were judged in advance to be science dependent and twelve were judged in advance to be foreign dependent. A peer group of 19 high level R&D managers was asked to rank all 24 technologies in terms of both their science and their foreign dependence. The bibliometric rankings of the technologies, based on their citations, were then compared with the peer rankings of the technologies.Overall, a high degree of agreement was found between the experts' opinion as to the science and foreign dependence of the areas and the corresponding bibliometric rankings. For example, the eight technologies judged most science dependent by experts averaged 0.92 cites per patent to scientific journal papers, while the eight technologies judged least science dependent had only 0.05 references per patent to journal papers. Similarly, large and statistically significant differences were found in the number of cites to foreign origin material for the eight technologies judged most foreign dependent by the experts when compared with the eight technologies judged least foreign dependent by the experts. These findings provide support for the hypothesis that patent citation data can be used in technological indicators development, and in technological policy analysis. They imply that citation-based location and analysis of science and foreign dependent technologies is a valid research tool when applied to the U.S. patent system.     

Analysis of the relationship between citation frequency of patents and diversity of their backward citations for Japanese patents

Conventional patent citation analyses have focused mainly on the presence of citation relationships, the number of patents cited by the subject patent, and the number of times the subject patent is cited by others (i.e., the numbers of backward and forward citations of the subject patent). However, most of them have not focused on patent classifications. Assuming that a patent based on a variety of technological bases tends to be an important patent that is cited more often, this study examines and clarifies the relationship between the diversity of classifications assigned to backward citations and the number of forward citations for Japanese patents. The results show notable differences in the number of classifications assigned to backward citations between the often cited and less frequently cited groups. It is considered that the diversity of backward citations can be utilized in the evaluation criteria for grouping that roughly identifies the often cited patents or eliminates a large part of less frequently cited patents.     

What makes the first forward citation of a patent occur earlier?

Identifying the economic value of a patent is crucial to technology management. It also facilitates the commercialization and transactions of patents. As a proxy of patent value, forward citation counting is widely used, but it takes a long time for a patent to be sufficiently cited. In this context, we suggest the first citation lag, namely the time taken until the first citation, as a proxy of patent value, as it is positively correlated with the patent value and considers the fact that important patents with a high economic value tend to receive many citations in a short space of time. We explore the influential patent attributes related to the first citation lag to build a model to predict the patent value. By using the Cox proportional hazard model on green inventory patent data, we find that patents with a shorter technology cycle time and a larger number of IPC four-digit classes, claims, patent family, and backward citations are associated with the shorter first citation lag, while a patent’s science linkage has an inverse U-shaped relationship with the first citation lag. Further, patents having an unconventional technological core have a longer first citation lag and among patents having an unconventional technological core, the presence of a novel element makes the first citation earlier. Our study is expected to help patent evaluation in the early stage of technology transfer.     

Patent-bibliometric analysis on the Chinese science — technology linkages

The purpose of this study is to explore the character and pattern of the linkage between science and technology in China, based on the database of United States Patent and Trademark Office (USPTO). The analysis is focused on the period 1995–2004, a rapid increasing period for Chinese US patents. Using the scientific non-patent references (NPRs) within patents, we investigate the science-technology connection in the context of Chinese regions as well as industrial sectors classified by International Patent Classification (IPC). 11 technological domains have been selected to describe the science intensity of the technology. The results suggest that the patents and the corresponding scientific citations are related in different ways. Finally, we match the scientific NPRs to the Science Citation Index (SCI) covered publications to identify the core journals and categories. It reveals that the scientific references covered by SCI show a skewed distribution not only in journals but also in categories.     

International earth science literature from Turkey — 1970–2005: Trends and possible causes

We investigated the publication trends in the international earth science literature coming out of Turkey in the period of 1970–2005 using the Science Citation Index Expanded database. A database of 2310 earth science publications with at least one of the authors with an address in Turkey was compiled. The number of earth science publications from Turkey shows a very rapid increase starting in the 1990’s in parallel with the increase in the total scientific output of Turkey. In the last decade the annual growth rate has been 16%. There was also a concomitant increase in the number of citations. The causes of the sharp increase in the publication numbers are, in order of importance, changes in the rules of academic promotion and appointment, changes in academic attitudes towards publishing, increasing support for research, financial incentives for publishing, and expansion of higher education. However, the sharp increase in the publication numbers was not accompanied by a similar increase in the impact of the publications as measured by the citations. Although publications with first authors from outside Turkey make up only 20% of the Turkish earth science publications in the period 1970–2005, these account for 38% of the total citations, and constitute 48 out of 100 most cited papers.     

Multiple regression analysis of a patent’s citation frequency and quantitative characteristics: the case of Japanese patents

Although many studies have been conducted to clarify the factors that affect the citation frequency of “academic papers,” there are few studies where the citation frequency of “patents” has been predicted on the basis of statistical analysis, such as regression analysis. Assuming that a patent based on a variety of technological bases tends to be an important patent that is cited more often, this study examines the influence of the number of cited patents’ classifications and compares it with other factors, such as the numbers of inventors, classifications, pages, and claims. Multiple linear, logistic, and zero-inflated negative binomial regression analyses using these factors are performed. Significant positive correlations between the number of classifications of cited patents and the citation frequency are observed for all the models. Moreover, the multiple regression analyses demonstrate that the number of classifications of cited patents contributes more to the regression than do other factors. This implies that, if confounding between factors is taken into account, it is the diversity of classifications assigned to backward citations that more largely influences the number of forward citations.     

Time relations between scientific production and patenting of knowledge: the case of nanotechnologies

Nanosciences and nanotechnologies are considered important for the development of science, technology and innovation, and the study of their characters can be a great help to the decisions of policy makers and of practitioners. This work is centred on the issue of the time relations between science and technology/innovation, and in particular on the speed of transfer of science-generated knowledge towards its exploitation in patenting. A methodology based on patent citations is used in order to measure the time lag between cited journal articles and citing patent, and thus the time proximity between the two steps. Keywords regarding nanotechnology/nanoscience items are searched in order to collect data useful for the analysis. Collateral measures, performed on another class of materials and on the spatial origin of citing/cited documents, help giving evidence of the peculiarity of the behaviour and on its nature. The most representative time lag between production of scientific knowledge and its technological exploitation appears being around 3–4 years.     

International scientific and technological collaboration of China from 2004 to 2008: a perspective from paper and patent analysis

Since China adopted Open-Up and Reformed Policy for global collaboration, China’s science and technology have experienced an astounding growth. Papers and patents encompass valuable scientific and technological (S&T) information and collaborative efforts. This article studies China’s international S&T collaboration from the perspective of paper and patent analysis. The results show that China’s total papers and patents have continuously increased from 2004 to 2008, the papers and patents resulting from China’s international collaboration also present a steady growth. However, there is a decline in the share of international collaboration papers and patents with a certain range due to the rapid independent R&D. China’s international scientific collaboration (ISC) is broadly distributed over many countries, the USA being the most important ISC partners. China’s international technological collaboration (ITC) is mainly carried out with USA and Taiwan, and Taiwan has been the most significant ITC partner of when taking countries’ patent output into account. Besides, ISC shows a continuous raise of Chinese papers’ citation. Even the countries with a small amount of papers and ISC with China, exert a positive influence on the impact of citation of Chinese papers as well. However, ITC does not always play an active role in the improvement of citation impact of Chinese patents.