Patent co-citation networks of Fortune 500 companies Xianwen Wang ��� Xi Zhang ��� Shenmeng Xu Received: 29 November 2010 / Published online: 25 May 2011 �� Akademiai �� Kiado, �� Budapest, Hungary 2011 Abstract This paper provides an overview of the progression of technology structure based on patent co-citation networks. Methods of patent bibliometrics, social network analysis and information visualization are employed to analyze patents of Fortune 500 companies indexed in Derwent Innovations Index, the largest patent database in the world. Based on the co-citation networks, several main technology groups are identified, including Chemicals, Petroleum Refining, Motor Vehicles, Pharmaceuticals, Electronics, etc. Rela- tionships among the leading companies and technology groups are also revealed. Keywords Fortune 500 Patent bibliometrics Patent co-citation Technology structure Introduction Fortune 500 are those leading companies in their industries according to the sales revenue ranked by Fortune magazine annually. These leading enterprises are intensive in patents, owing to the great emphasis they put on technological innovation for retaining the com- petitive advantages in corresponding industries. Because of the representativeness for the whole technology frontier around the world, we have great interest in conducting our analysis on patents of these companies. Patents are becoming increasingly important to commercial organizations, especially for multinational companies. According to the report of World Intellectual Property Organization, nearly 90���95% of the world���s R&D outcomes are covered in patent publi- cations, only the rest 5���10% are included in the scientific literatures (papers and mono- graphs) (Liu and Yang 2008). Patents, which contain a great amount of knowledge on technical innovations, provide a valuable source of information on technology development and innovative activities (Li et al. 2009). It is crucial to analyze patent information to understand industrial trends and set the future developing directions. X. Wang (&) X. Zhang S. Xu WISE Lab, Dalian University of Technology, Dalian, China e-mail: xianwenwang@dlut.edu.cn 123 Scientometrics (2011) 88:761���770 DOI 10.1007/s11192-011-0414-x

Literature review Patent bibiliometrics The idea of using bibliometrics methods for analyzing patent information could be dated back to 1940s, when Arthur H. Seidel proposed a citation index of the patent literatures in the Journal of the Patent Office Society and Harry C. Hart endorsed the idea in a later issue (Garfield and Merton 1979). Although this idea was brought up at that time, neither patent citation nor other bibliometrics methods were broadly applied to patent literature analysis until the last decade in 20th century. With his pioneering work on patent citations, Narin opened up a new field of application for bibliometrics methods to patents. He extended the existing interpretative framework for citations in research papers to the field of patent citations successfully (Narin 1994). Most of the previous works using the patent bibliometrics methods mainly deal with three issues, the productivity, impact and correlation. Patent counting is the most common method used to measure the productivity. Patented innovations which are particularly novel will be the subject of greater citations. For this reason, the number of citations received by a patent is used in the literature as a measure of the innovative output embodied in technology. By counting the number of patents granted each year, the growth of the research productivity could be drawn. The method was applied to analyzing the productivity on countries, assignees, inventors (Narin 1994, 1995 Narin et al. 1994 Karki 1997) and technology levels (Ramani and De Looze 2002 Lopez-Munoz et al. 2003). As for the studies of research impact, citation count is used as an indicator to present the level of impact (Moed 2000 Albert and Plaza 2004). Except for the cited patent count, counting numbers of shared patent citations, as well as patent coupling, were applied to establishing the technological relationships among countries, assignees, inventor and techniques (Lo 2007, 2008). Patent citation analysis Generally speaking, there are three types of citations (Small 1997): direct citation, and the other two indirect citation, namely co-citation (Small 1973), and bibliographic coupling (Kessler 1963). Citation analysis has its origins within bibliometrics, i.e., the study of citation behaviors on behalf of scientific authors or academic journals. A considerable amount of research has been done to identify the similarities and differences between scientific literature and patent (Meyer 2000). A patent citation indicates that an innovation may be partly based on an earlier patented one. All ������prior art������ related to the patented invention are required to be disclosed. Patent citations allow the analyst to assess the quality and impact of cited material, as well as the linkages between cited and citing countries, between cited and citing companies, and between cited and citing scientific and technological areas (Narin and Olivastro 1988). Patent co-citation analysis Co-citation analysis, firstly introduced by Herry Small in 1973, is the most influential technique in bibliometrics, which is used widely for macro S&T policy planning and evaluation. 762 X. Wang et al. 123